- Email: [email protected]
Differences in myosin heavy-chain composition between human jaw-closing muscles and supra- and infrahyoid muscles
Archives of Oral Biology 46 (2001) 821– 827 www.elsevier.com/locate/archoralbio
Differences in myosin heavy-chain composition between human jaw-closing muscles and supra- and infrahyoid muscles J.A.M. Korfage *, Y.T. Schueler, P. Brugman, T.M.G.J. Van Eijden Department of Functional Anatomy, Academic Center for Dentistry Amsterdam (ACTA), Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands Accepted 20 March 2001
Abstract Jaw-closing muscles have architectural features suited to force production; supra- and infrahyoid muscles are better adapted to produce velocity and displacement. It was hypothesized that this difference in function would be reflected in myosin heavy-chain (MyHC) composition (equivalent to contraction velocity) and fibre-type cross-sectional area (equivalent to force). MyHC composition was determined in muscles obtained from eight human cadavers, using monoclonal antibodies against MyHC isoforms. Jaw closers contained 4.2 times fewer type IIA fibres and 5.2 times more hybrid fibres than suprahyoid muscles, and 3.9 times fewer type IIA fibres and 3.2 times more hybrid fibres than the infrahyoid muscles. In the jaw closers, MyHC-I was expressed in approx. 70% of all fibres (pure + hybrid), in the suprahyoid muscles in approx. 40%, and in the infrahyoid muscles in approx. 46%. In the jaw closers, type I fibres were 40% larger in diameter than in the supra- and infrahyoid muscles. It can be concluded that the jaw closers have characteristics of slow muscles, and that the supra-/infrahyoid muscles have characteristics of fast muscles. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Fibre type; Human; Mastication
1. Introduction The jaw-closing muscles are characterized by relatively large physiological cross-sectional areas, large percentages of tendinous tissue, short fibres and large pennation angles. The supra- and infrahyoid muscles, however, show the opposite characterictics (for the architectural design of jaw closers and openers, see Van Eijden et al., 1997). Therefore, the jaw closers are capable of producing larger forces than the supra-/inAbbre6iations: MyHC, myosin heavy chain. * Corresponding author. Tel.: + 31-20-5665357; fax: + 3120-6911856. E-mail address: [email protected] (J.A.M. Korfage).
frahyoid muscles, which in turn are capable of producing larger excursions and higher shortening velocities. This difference is also seen in other antagonistic muscle groups such as knee extensors and flexors, as well as ankle plantarflexors and dorsiflexors (Wickiewicz et al., 1983; Lieber and Blevins, 1989). The force– velocity properties of muscle fibres are mainly dependent on their MyHC contents (Bottinelli et al., 1996). Muscle fibres expressing MyHC type I are slow-contracting, and fibres expressing MyHC-IIA or -IIX are fast-contracting; myosin MyHC-IIX fibres contract more quickly than IIA fibres. MyHC-IIB is said to be absent in man, although its gene has recently been cloned (Weiss et al., 1999). Muscle fibres can contain either one single MyHC or a combination of
0003-9969/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 3 - 9 9 6 9 ( 0 1 ) 0 0 0 4 2 - 5
822
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
different ones (Pette and Staron, 1990). In the combination fibres, a continuum of physiological properties can be observed (Schiaffino and Reggiani, 1994; Kwa et al., 1995). Compared to limb and trunk muscles, human masticatory muscle fibres can express two distinct MyHCs, in combination with one or more of the aforementioned MyHCs. First, MyHC-fetal, which is normally expressed in developing muscle fibres (ButlerBrowne et al., 1988) and has been shown to increase during ageing in the masseter (Monemi et al., 1999), and secondly, MyHC-cardiac-a, which is normally expressed in the atrium of the heart (Bredman et al., 1991). The amount of force that a muscle fibre is capable of producing is proportional to its cross-sectional area. This area is usually related to the fibre type and the amount of resistance that is experienced during contraction (Edgerton et al., 1995; McCall et al., 1996). Our aim now was to compare the immunohistochemical and morphological properties of the human jaw-closing and supra-/infrahyoid muscles. As the jaw closers and the supra-/infrahyoid muscle group have different functions, we examined whether their fibre-type compositions and cross-sectional areas were different. It was hypothesized that, because of their different functions, the supra-/infrahyoid muscles would contain more fasttype MyHCs and have smaller fibre cross-sectional areas than the jaw-closing muscles.
2. Materials and methods Jaw-closing muscles (temporalis, masseter, lateral and medial pterygoid) and suprahyoid muscles (mylohyoid, stylohyoid, geniohyoid, and digastic) were obtained from eight Caucasian cadavers (five males and three females, mean age 9S.D., 71.6 9 15.0 years). In six of these cadavers (four males and two females), the infrahyoid muscles (sternohyoid, sternothyroid, thyrohyoid, and omohyoid) were used. Six of the eight cadavers had full upper and lower dental prostheses, and two were partially dentate. The muscles were obtained within 12 –36 h of death. This use of human muscles conforms to a written protocol that was reviewed and approved by the Department of Anatomy and Embryology of the Academic Medical Center of the University of Amsterdam. After the muscles had been exposed, they were cut from their attachment sites. The following muscles or muscle portions were removed separately: anterior and posterior temporalis, masseter, medial pterygoid, superior and inferior head of the lateral pterygoid, mylohyoid, stylohyoid, geniohyoid, anterior and posterior belly of the digastric, sternohyoid, sternothyroid, thyrohyoid and superior belly of the omohyoid. The unfixed muscles were rapidly frozen in liquid nitrogen-cooled
isopentane and stored at − 80°C until required for further processing.
2.1. Immunohistochemistry Serial transverse sections of 10 mm were cut in a cryomicrotome. They were obtained from the belly of the muscles perpendicular to the main direction of the fibres. In the masseter, the sections were taken at approx. 0.5 cm from the attachment to the zygomatic arch to ensure that the deep masseter was included. For the mylohyoid, care was taken that the part of the muscle attaching to the hyoid bone was included. After overnight fixation at − 20°C in a mixture of methanol:acetone:acetic acid:water (35:35:5:25), the sections were incubated with monoclonal antibodies raised against purified myosin (Bredman et al., 1991; Sant’Ana Pereira et al., 1995). Antibody 219-1D1 recognized MyHC-I, antibody 249-5A4 recognized MyHC-cardiac-a, antibody 333-7H1 recognized MyHC-IIA, and antibody 332-3D4 recognized MyHCIIA and MyHC-IIX. The specificity and characterization of these monoclonal antibodies against human MyCh isoforms have been demonstrated elsewhere (Wessels et al., 1991; Sant’Ana Pereira et al., 1995); those studies showed that human ATPase-defined type I and type IIA muscle fibres reacted with antibodies against MyHC-I and MyHC-IIA, respectively, and that human ATPase-defined type IIB muscle fibres contained a MyHC isoform that was homologous to the MyHC-IIX isoform of rodents. In the present study, we classified the fibres according to the MyHCs they expressed. Thus, the type I and IIA fibres mentioned here were fibres expressing only MyHC-I and MyHC-IIA, respectively, and the type IIX fibres were fibres expressing only MyHC-IIX. Hybrid fibres were those that expressed more than one isoform. Antifetal MyHC was purchased from Novocastra Laboratories (Newcastle upon Tyne, UK). The indirect unconjugated immunoperoxidase (PAP) technique was applied to detect the specific binding of the different antibodies. Nickel – diaminobenzidine was used to visualize the staining.
2.2. Sample method, fibre-type classification and cross-sectional area measurements From each muscle, a number of areas were sampled; the number of samples was dependent on the size of the muscles (jaw closers, six to nine; suprahyoid muscles, four; infrahyoid muscles, two to four). In each muscle, the samples were taken across the section at equal anteroposterior, mediolateral, or craniocaudal distances from each other. In each sample area (about 0.6 –0.4 mm), 50–450 fibres (average 178.6) were drawn by means of a projection microscope (Carl Zeiss, Oberkochen, Germany) and a mirror table, on to a
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
transparent sheet. Each fibre was classified by means of a series of six consecutive incubated sections. Fibres not recognized in each of these six sections were omitted. In an earlier study (Korfage and Van Eijden, 1999), we determined the reproducibility of this classification method. It appeared that 6.6% of the fibres compared gave conflicting results because in these, the antibody staining was not reproducible. In half of these fibres, MyHC-cardiac-a was not reproducible. The cross-sectional area of the fibres was measured by reading the drawn sheets, together with a grade mark for correction of enlargement, via a flat-bed scanner (Hewlett-Packard, Scanjet 4c) into a personal computer. A custom-made program computed the cross-sectional area of each fibre from the reproduced image. In total, more than 60 000 fibres were analysed in all muscles.
823
types were found, with various combinations of isoforms. The most abundant hybrid fibre types in the jaw closers were fibres expressing cardiac-a+ I+ IIA (9.7%), cardiac-a+ IIA (5.9%), I + IIA (4.9%), and cardiac-a+ I (4.0%). The proportion of other fibre types was lower than 2% in the jaw closers and 0.5% in the supra-/infrahyoid muscles and showed a large variance amongst individuals. In the suprahyoid muscles, the
2.3. Statistical analysis A distinction was made between pure fibre types that express one isoform and hybrid fibre types that express more than one isoform. For each muscle, the relative amount of the various pure and hybrid fibres was determined. To compare differences in fibre size, the cross-sectional area of these fibres was measured and related to their MyHC content. For each individual, the mean fibre-type distribution and cross-sectional area were calculated in the jaw closers and the suprahyoid and infrahyoid muscles. Then, the means of these three groups were calculated over all individuals. As the fibre-type distribution of the lateral pterygoid had more similarities with that of the jaw closers than with the jaw openers (Korfage and Van Eijden, 2000), we have included this muscle among the group of jaw closers. Differences in fibre-type distribution and in fibre crosssectional area of a particular MyHC isoform between muscle groups were analysed by the Wilcoxon signed ranking test for paired data. The level of significance was set to PB0.05.
3. Results The percentage of a particular fibre type did not differ significantly among the muscles of a particular group. The three muscle groups contained, on average, equal percentages of pure type I and type IIX fibres (Fig. 1). In contrast, the percentages of pure type IIA and hybrid fibres differed significantly between the jaw closers and the supra-/infrahyoid muscle groups. The supra- and infrahyoid muscles contained more type IIA fibres, whereas the jaw closers contained more hybrid fibres. In the three muscle groups, MyHC-fetal or cardiac-a were only found in hybrid fibres, in combination with one or more isoforms. Many different hybrid fibre
Fig. 1. Fibre-type composition (mean 9 S.D.) in human jaw closers, supra- and infrahyoid muscles. S.D. values are a measure of interindividual variability. MyHC, myosin heavy chain.
824
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
Fig. 2. Total proportion of fibres (mean 9 S.D.) expressing a given myosin heavy chain (MyHC) isoform in pure + hybrid fibres in jaw closers, supra- and infrahyoid muscles.
most abuntant hybrid fibre types were fibres expressing cardiac-a+IIA (2.0%), cardiac-a+I (1.5%), and I + IIA (1.3%), and in the infrahyoid muscles, fibres expressing cardiac-a+IIA (6.6%) and I +IIA (1.4%). The total amount of fibres (pure +hybrid) expressing a particular isoform showed that MyHC-I was expressed in about 70% of all fibres in the jaw closers, while this isoform was expressed in about 40% of all fibres in the suprahyoid muscles and in about 46% of all fibres in the infrahyoid muscles (Fig. 2). The supra-/ infrahyoid muscles contained significantly more fibres (about 50%) that expressed MyHC-IIA than the jaw closers (about 30%). Furthermore, jaw closers contained more fibres expressing MyHC-fetal or MyHCcardiac-a (10 and 25%, respectively) than the suprahyoid muscles (1 and 5%, respectively) and infrahyoid muscles (1 and 9%, respectively). These two isoforms showed a high interindividual variability. In the jaw-closing muscles, type I fibres were significantly larger (40%) than in the supra- and infrahyoid muscles (Fig. 3). No significant difference was seen in the cross-sectional area between other fibre types. Within the group of jaw closers, type I fibres were about 40% larger than other fibre types. This difference was not seen within the supra-/infrahyoid muscles.
4. Discussion This is, to the best of our knowledge, the first study to compare fibre-type distributions and cross-sectional areas amongst the jaw closers and the supra- and infrahyoid muscles in one group of human individuals. Within the groups, no large difference was seen in
fibre-type distribution or cross-sectional area (for jaw closers and openers, see Korfage et al., 2000). The fibre-type distributions and fibre cross-sectional areas of the human jaw muscles reported here and in other studies (Ringqvist, 1973; Vignon et al., 1980; Eriksson et al., 1982; Ringqvist et al., 1982; Eriksson and Thornell, 1983; Sciote et al., 1994; Uhlig et al., 1995; Monemi et al., 1999) are different from what is commonly found in limb and trunk muscles (Johnson et al., 1973; Polgar et al., 1973). Compared to those muscles, masticatory muscles have more hybrid fibres, many of them coexpressing MyHC-fetal and/or cardiac-a (Korfage and Van Eijden, 1999, 2000; Korfage et al., 2000). Furthermore, jaw muscle fibres have smaller cross-sectional areas. In human masticatory muscles, type I fibres are reportedly larger than type II fibres, while in limb and trunk muscles, the opposite is true (Ringqvist, 1974). However, the type I fibres in human jaw-closing muscle are not large in absolute terms; rather, the type II fibres are often unusually small. The present results indicate that these differences are more pronounced for jaw-closing than for supra- and infrahyoid muscles, as the supra-/infrahyoid muscles had fewer hybrid fibres than the jaw-closing muscles and type I fibres in the supra-/infrahyoids were not larger than type II fibres. Several explanations have been suggested for this difference between masticatory muscles and limb and trunk muscles, including differences in their function and/or nerve supply (Butler-Browne et al., 1988; Sta˚ l et al., 1994), differences in their genetic pathways for expressing muscle-specific proteins during embryogenesis, and differences in their chronological or spatial activation of some transcription factors (Marcucio and Noden, 1999).
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
The jaw closers and the supra-/infrahyoid muscles have different functions. In general, the jaw closers contract more slowly and experience more resistance during trituration of food than the supra- and infrahyoids. The jaw closers also exhibit continuous low-level electromyographic activity to maintain the mandibular rest position (Miller, 1991). In an earlier study, we demonstrated that jaw closers have architectural features that suit them to force production, whereas the suprahyoid muscles are better designed to produce larger excursions and larger velocities (Van Eijden et al., 1997). The present results indicate that such a specialization is reflected in the fibre-type composition of all three muscle groups. The jaw closers had more fibres expressing MyHC-I (pure +hybrid), whereas the supra- and infrahyoid muscles had more fibres expressing MyHC-IIA. Type I fibres, which express MyHC-I, contract more slowly than type II fibres, which express MyHC-IIA or IIX. Therefore, the jaw closers can be considered as slower than the supra-/infrahyoid muscles. According to the size principle (Henneman et al., 1965), type I motor units are recruited first in a motor task, whereas type II motor units are recruited when higher velocities or forces are required. The same recruitment order is applicable to human jaw muscles (Yemm, 1977; Scutter and Tu¨ rker, 1998). The jaw closers possess more fibres expressing MyHC-I, and the supra- and infrahyoid muscles possess more fibres expressing MyHC-II; this suggests that the jaw closers are more suited to displaying tonic activity, whereas the supra-/infrahyoid muscles are more suited to displaying phasic activity. Furthermore, type I motor units have
825
smaller innervation ratios than type II units (Burke and Tsairis, 1973). Therefore, it can be expected that the jaw closers will be better equipped to regulate the magnitude of the force produced during chewing or biting than the supra- and infrahyoid muscles. The exact proportion of individual MyHC isoforms within single hybrid fibres remains to be investigated. Another factor that might contribute to this better force-regulating capacity of the jaw closers is their higher proportion of hybrid fibres. Studies on the contractile properties of single muscle fibres and motor units expressing multiple MyHCs have shown that the coexpression of different MyHC isoforms yields a greater variance in shortening velocities and force generation than is possible in pure fibres (Johnson et al., 1994; Kwa et al., 1995; Sciote and Kentish, 1996). We also found that, in the jaw closers, the cross-sectional area of type I fibres was approx. 40% greater than in the supra-/infrahyoid muscles and that, in the jaw closers, type I fibres were larger than type II and hybrid fibres. The larger cross-sectional area of type I fibres compared to other fibre types confirms the findings of others (Ringqvist, 1974; Vignon et al., 1980; Eriksson and Thornell, 1983). These larger cross-sectional areas might be the result of the larger resistance experienced by the jaw closers during chewing. Training against resistance causes an increase in fibre cross-sectional area (McCall et al., 1996), while weightlessness causes a decrease (Edgerton et al., 1995). As we used material from elderly individuals, which might not have the same phenotype as young adults, we have compared our data with those from other studies in which masticatory muscles of either young or old
Fig. 3. Fibre-type cross-sectional area (mean 9 S.D.) of the jaw closers, supra- and infrahyoid muscles. S.D. values are a measure for interindividual variability. MyHC, myosin heavy chain.
826
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
individuals were examined. From this comparison, it appears that young individuals have more type I and fewer hybrid fibres than elderly individuals, suggesting that the proportion of type I fibres decreases, and that of hybrid fibres increases with age (Vignon et al., 1980; Eriksson and Thornell, 1983; Monemi et al., 1999; Korfage et al., 2000). The variability in fibre-type proportion and cross-sectional area was relatively large. Possible explanations are (1) the samples were drawn from heterogeneous populations; (2) differences in facial morphology; (3) difference in the usage of the muscles; (4) difference in the age of the individuals. Acknowledgements This research was supported institutionally by the Interuniversitary Research School of Dentistry, through the Academic Centre of Dentistry Amsterdam. We would like to express our gratitude to L.J. van Ruijven for the technical support and J. Ruijter for statistical advice. References Bottinelli, R., Caneparri, M., Pellegrino, M.A., Reggiani, C., 1996. Force – velocity properties of human skeletal muscle fibres: myosin heavy chain isoforms and temperature dependence. J. Physiol. 495, 573 –586. Bredman, J.J., Wessels, A., Weijs, W.A., Korfage, J.A.M., Soffers, C.A.S., Moorman, A.F.M., 1991. Demonstation of ‘cardiac-specific’ myosin heavy chain in masticatory muscles of human and rabbit. Histochem. J. 23, 160 –170. Burke, R.E., Tsairis, P., 1973. Anatomy and innervation ratios in motor units of cat gastrocnemius. J. Physiol. 234, 749 – 765. Butler-Browne, G.S., Eriksson, P.-O., Laurent, C., Thornell, L.-E., 1988. Adult human masseter muscle fibres express myosin isozymes characteristic of development. Muscle and Nerve 11, 610 – 620. Edgerton, V.R., Zhou, M.-Y., Ohira, Y., Klitgaard, H., Jiang, B., Bell, G., Harris, B., Saltin, B., Gollnick, P.D., Roy, R.R., Day, M.K., Greenisen, M., 1995. Human fiber size and enzymatic properties after 5 and 11 days of spaceflight. J. Appl. Physiol. 78, 1733 –1739. Eriksson, P.-O., Eriksson, A., Ringqvist, M., Thornell, L.-E., 1982. Histochemical fibre composition of the human digastric muscle. Arch. Oral Biol. 27, 207 –215. Eriksson, P.-O., Thornell, L.-E., 1983. Histochemical and morphological muscle-fibre characteristics of the human masseter, the medial pterygoid and the temporal muscle. Arch. Oral Biol. 28, 781 –795. Henneman, E., Somjen, G., Carpenter, D.O., 1965. Functional significance of cell size in spinal motoneurons. J. Neurophysiol. 28, 560 – 580. Johnson, M.A., Polgar, J., Weightman, D., Appleton, D., 1973. Data on the distribution of fibre types in thirty-six human muscles. An autopsy study. J. Neurol. Sci. 18, 111 – 129.
Johnson, B.D., Wilson, L.E., Zhan, W.Z., Watchko, J.F., Daood, M.J., Sieck, G.C., 1994. Contractile properties of the developing diaphragm correlate with myosin heavy chain phenotype. J. Appl. Physiol. 77, 481 – 487. Korfage, J.A.M., Van Eijden, T.M.G.J., 1999. Regional differences in fibre type composition in the human temporalis muscle. J. Anat. 194, 355 – 362. Korfage J.A.M., Van Eijden T.M.G.J., 2000. Myosin isoform composition of the human medial and lateral pterygoid muscles. J. Dent. Res, 79, 1618 – 1625. Korfage J.A.M., Brugman P., Van Eijden T.M.G.J., 2000. Intermuscular and intramuscular differences in myosin heavy chain composition of the human masticatory muscles. J. Neurol. Sci, 178, 95 – 106. Kwa, S.H.S., Weijs, W.A., Ju¨ gh, P.J.W., 1995. Contraction characteristics and myosin heavy chain composition of rabbit masseter motor units. J. Neurophysiol. 73, 538 – 549. Lieber, R.L., Blevins, F.T., 1989. Skeletal muscle architecture of the rabbit hindlimb: functional implications of muscle design. J. Morphol. 199, 93 – 101. McCall, G.E., Byrnes, W.C., Dickinson, A., Pattany, P.M., Fleck, S.J., 1996. Muscle fiber hypertrophy, hyperplasia, and capillary density in college men after resistance training. J. Appl. Physiol. 81, 2004 – 2012. Marcucio, R.S., Noden, D.M., 1999. Myotube heterogeneity in developing chick craniofacial skeletal muscles. Dev. Dynam. 214, 178 – 194. Miller, A.J., 1991. Craniomandibular Muscles: Their Role in Function and Form. CRC Press, Boca Raton, FL. Monemi, M., Eriksson, P.-O., Kadi, F., Butler-Browne, G.S., Thornell, L.-E., 1999. Opposite changes in myosin heavy chain composition of human masseter and biceps brachii muscles during aging. J. Muscle Res. Cell Motil. 20, 351 – 361. Pette, D., Staron, R.S., 1990. Cellular and molecular diversities of mammalian skeletal muscle fibres. Rev. Physiol. Biochem. Pharmacol. 116, 2 – 76. Polgar, J., Johnson, M.A., Weightman, D., Appleton, D., 1973. Data on fibre size in thirty-six human muscles. An autopsy study. J. Neurol. Sci. 19, 307 – 318. Ringqvist, M., 1973. Fibre sizes of human masseter muscle in relation to bite force. J. Neurol. Sci. 19, 297 – 305. Ringqvist, M., 1974. Fiber types in human masticatory muscles. Relation to function. Scand. J. Dent. Res. 82, 333 – 355. Ringqvist, M., Ringqvist, I., Eriksson, P.-O., Thornell, L.-E., 1982. Histochemical fibre-type profile in the human masseter muscle. J. Neurol. Sci. 53, 273 – 282. Sant’Ana Pereira, J.A.A., Wessels, A., Nijtmans, L., Moorman, A.F.M., Sargeant, A.J., 1995. New method for the accurate characterization of single human skeletal muscle fibres demonstrates a relation between mATPase and MyHC expression in pure and hybrid fibre types. J. Muscle Res. Cell Motil. 16, 21 – 34. Schiaffino, S., Reggiani, C., 1994. Myosin isoforms in mammalian skeletal muscle. J. Appl. Physiol. 77, 493 – 501. Sciote, J.J., Rowlerson, A.M., Hopper, C., Hunt, N.P., 1994. Fibre type classification and myosin isoforms in the human masseter muscle. J. Neurol. Sci. 126, 15 – 24. Sciote, J.J., Kentish, J.C., 1996. Unloading shortening velocities of rabbit masseter muscle fibres expressing skeletal or a-cardiac myosin heavy chains. J. Physiol. 492, 659 – 667.
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827 Scutter, S.D., Tu¨ rker, K.S., 1998. Recruitment stability in masseter motor units during isometric voluntary contractions. Muscle and Nerve 21, 1290 –1298. Sta˚ l, P., Eriksson, P.-O., Schiaffino, S., Butler-Browne, G.S., Thornell, L.-E., 1994. Differences in myosin composition between human oro-facial, masticatory, and limb muscles: enzyme-, immunohisto- and biochemical studies. J. Muscle Res. Cell Motil. 15, 517 – 534. Uhlig, Y., Weber, B.R., Grob, D., Muntener, M., 1995. Fiber composition and fiber transformations in neck muscles of patients with dysfunction of the cervical spine. J. Orthopaed. Res. 13, 240 – 249. Van Eijden, T.M.G.J., Korfage, J.A.M., Brugman, P., 1997. Architecture of the human jaw-closing and jaw-opening muscles. Anat. Rec. 248, 464 –474. Vignon, C., Pellissier, J.F., Serratrice, G., 1980. Further histochemical studies on masticatory muscles. J. Neurol. Sci. 45, 157 – 176.
.
827
Weiss, A., Schiaffino, S., Leinwand, L.A., 1999. Comparative sequence analysis of the complete human sarcomeric myosin heavy chain family: implications for functional diversity. J. Mol. Biol. 290, 61 – 75. Wessels, A., Vermeulen, J.L.M., Viragh, Sz., Ka´ lma´ n, F., Lamers, W.H., Moorman, A.F.M., 1991. Spatial distribution of ‘tissue specific’ antigens in the developing human heart and skeletal muscle. II. An immunohistochemical analysis of myosin heavy chain isoform expression patterns in the embryonic heart. Anat. Rec. 229, 355 – 368. Wickiewicz, T.L., Roy, R.R., Powell, P.L., Edgerton, V.R., 1983. Muscle architecture of the human lower limb. Clin. Orthopaed. Relat. Res. 179, 275 – 283. Yemm, R., 1977. The orderly recruitment of motor units of the masseter and temporal muscles during voluntary isometric contraction in man. J. Physiol. 265, 163 – 174.
Differences in myosin heavy-chain composition between human jaw-closing muscles and supra- and infrahyoid muscles J.A.M. Korfage *, Y.T. Schueler, P. Brugman, T.M.G.J. Van Eijden Department of Functional Anatomy, Academic Center for Dentistry Amsterdam (ACTA), Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands Accepted 20 March 2001
Abstract Jaw-closing muscles have architectural features suited to force production; supra- and infrahyoid muscles are better adapted to produce velocity and displacement. It was hypothesized that this difference in function would be reflected in myosin heavy-chain (MyHC) composition (equivalent to contraction velocity) and fibre-type cross-sectional area (equivalent to force). MyHC composition was determined in muscles obtained from eight human cadavers, using monoclonal antibodies against MyHC isoforms. Jaw closers contained 4.2 times fewer type IIA fibres and 5.2 times more hybrid fibres than suprahyoid muscles, and 3.9 times fewer type IIA fibres and 3.2 times more hybrid fibres than the infrahyoid muscles. In the jaw closers, MyHC-I was expressed in approx. 70% of all fibres (pure + hybrid), in the suprahyoid muscles in approx. 40%, and in the infrahyoid muscles in approx. 46%. In the jaw closers, type I fibres were 40% larger in diameter than in the supra- and infrahyoid muscles. It can be concluded that the jaw closers have characteristics of slow muscles, and that the supra-/infrahyoid muscles have characteristics of fast muscles. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Fibre type; Human; Mastication
1. Introduction The jaw-closing muscles are characterized by relatively large physiological cross-sectional areas, large percentages of tendinous tissue, short fibres and large pennation angles. The supra- and infrahyoid muscles, however, show the opposite characterictics (for the architectural design of jaw closers and openers, see Van Eijden et al., 1997). Therefore, the jaw closers are capable of producing larger forces than the supra-/inAbbre6iations: MyHC, myosin heavy chain. * Corresponding author. Tel.: + 31-20-5665357; fax: + 3120-6911856. E-mail address: [email protected] (J.A.M. Korfage).
frahyoid muscles, which in turn are capable of producing larger excursions and higher shortening velocities. This difference is also seen in other antagonistic muscle groups such as knee extensors and flexors, as well as ankle plantarflexors and dorsiflexors (Wickiewicz et al., 1983; Lieber and Blevins, 1989). The force– velocity properties of muscle fibres are mainly dependent on their MyHC contents (Bottinelli et al., 1996). Muscle fibres expressing MyHC type I are slow-contracting, and fibres expressing MyHC-IIA or -IIX are fast-contracting; myosin MyHC-IIX fibres contract more quickly than IIA fibres. MyHC-IIB is said to be absent in man, although its gene has recently been cloned (Weiss et al., 1999). Muscle fibres can contain either one single MyHC or a combination of
0003-9969/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 3 - 9 9 6 9 ( 0 1 ) 0 0 0 4 2 - 5
822
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
different ones (Pette and Staron, 1990). In the combination fibres, a continuum of physiological properties can be observed (Schiaffino and Reggiani, 1994; Kwa et al., 1995). Compared to limb and trunk muscles, human masticatory muscle fibres can express two distinct MyHCs, in combination with one or more of the aforementioned MyHCs. First, MyHC-fetal, which is normally expressed in developing muscle fibres (ButlerBrowne et al., 1988) and has been shown to increase during ageing in the masseter (Monemi et al., 1999), and secondly, MyHC-cardiac-a, which is normally expressed in the atrium of the heart (Bredman et al., 1991). The amount of force that a muscle fibre is capable of producing is proportional to its cross-sectional area. This area is usually related to the fibre type and the amount of resistance that is experienced during contraction (Edgerton et al., 1995; McCall et al., 1996). Our aim now was to compare the immunohistochemical and morphological properties of the human jaw-closing and supra-/infrahyoid muscles. As the jaw closers and the supra-/infrahyoid muscle group have different functions, we examined whether their fibre-type compositions and cross-sectional areas were different. It was hypothesized that, because of their different functions, the supra-/infrahyoid muscles would contain more fasttype MyHCs and have smaller fibre cross-sectional areas than the jaw-closing muscles.
2. Materials and methods Jaw-closing muscles (temporalis, masseter, lateral and medial pterygoid) and suprahyoid muscles (mylohyoid, stylohyoid, geniohyoid, and digastic) were obtained from eight Caucasian cadavers (five males and three females, mean age 9S.D., 71.6 9 15.0 years). In six of these cadavers (four males and two females), the infrahyoid muscles (sternohyoid, sternothyroid, thyrohyoid, and omohyoid) were used. Six of the eight cadavers had full upper and lower dental prostheses, and two were partially dentate. The muscles were obtained within 12 –36 h of death. This use of human muscles conforms to a written protocol that was reviewed and approved by the Department of Anatomy and Embryology of the Academic Medical Center of the University of Amsterdam. After the muscles had been exposed, they were cut from their attachment sites. The following muscles or muscle portions were removed separately: anterior and posterior temporalis, masseter, medial pterygoid, superior and inferior head of the lateral pterygoid, mylohyoid, stylohyoid, geniohyoid, anterior and posterior belly of the digastric, sternohyoid, sternothyroid, thyrohyoid and superior belly of the omohyoid. The unfixed muscles were rapidly frozen in liquid nitrogen-cooled
isopentane and stored at − 80°C until required for further processing.
2.1. Immunohistochemistry Serial transverse sections of 10 mm were cut in a cryomicrotome. They were obtained from the belly of the muscles perpendicular to the main direction of the fibres. In the masseter, the sections were taken at approx. 0.5 cm from the attachment to the zygomatic arch to ensure that the deep masseter was included. For the mylohyoid, care was taken that the part of the muscle attaching to the hyoid bone was included. After overnight fixation at − 20°C in a mixture of methanol:acetone:acetic acid:water (35:35:5:25), the sections were incubated with monoclonal antibodies raised against purified myosin (Bredman et al., 1991; Sant’Ana Pereira et al., 1995). Antibody 219-1D1 recognized MyHC-I, antibody 249-5A4 recognized MyHC-cardiac-a, antibody 333-7H1 recognized MyHC-IIA, and antibody 332-3D4 recognized MyHCIIA and MyHC-IIX. The specificity and characterization of these monoclonal antibodies against human MyCh isoforms have been demonstrated elsewhere (Wessels et al., 1991; Sant’Ana Pereira et al., 1995); those studies showed that human ATPase-defined type I and type IIA muscle fibres reacted with antibodies against MyHC-I and MyHC-IIA, respectively, and that human ATPase-defined type IIB muscle fibres contained a MyHC isoform that was homologous to the MyHC-IIX isoform of rodents. In the present study, we classified the fibres according to the MyHCs they expressed. Thus, the type I and IIA fibres mentioned here were fibres expressing only MyHC-I and MyHC-IIA, respectively, and the type IIX fibres were fibres expressing only MyHC-IIX. Hybrid fibres were those that expressed more than one isoform. Antifetal MyHC was purchased from Novocastra Laboratories (Newcastle upon Tyne, UK). The indirect unconjugated immunoperoxidase (PAP) technique was applied to detect the specific binding of the different antibodies. Nickel – diaminobenzidine was used to visualize the staining.
2.2. Sample method, fibre-type classification and cross-sectional area measurements From each muscle, a number of areas were sampled; the number of samples was dependent on the size of the muscles (jaw closers, six to nine; suprahyoid muscles, four; infrahyoid muscles, two to four). In each muscle, the samples were taken across the section at equal anteroposterior, mediolateral, or craniocaudal distances from each other. In each sample area (about 0.6 –0.4 mm), 50–450 fibres (average 178.6) were drawn by means of a projection microscope (Carl Zeiss, Oberkochen, Germany) and a mirror table, on to a
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
transparent sheet. Each fibre was classified by means of a series of six consecutive incubated sections. Fibres not recognized in each of these six sections were omitted. In an earlier study (Korfage and Van Eijden, 1999), we determined the reproducibility of this classification method. It appeared that 6.6% of the fibres compared gave conflicting results because in these, the antibody staining was not reproducible. In half of these fibres, MyHC-cardiac-a was not reproducible. The cross-sectional area of the fibres was measured by reading the drawn sheets, together with a grade mark for correction of enlargement, via a flat-bed scanner (Hewlett-Packard, Scanjet 4c) into a personal computer. A custom-made program computed the cross-sectional area of each fibre from the reproduced image. In total, more than 60 000 fibres were analysed in all muscles.
823
types were found, with various combinations of isoforms. The most abundant hybrid fibre types in the jaw closers were fibres expressing cardiac-a+ I+ IIA (9.7%), cardiac-a+ IIA (5.9%), I + IIA (4.9%), and cardiac-a+ I (4.0%). The proportion of other fibre types was lower than 2% in the jaw closers and 0.5% in the supra-/infrahyoid muscles and showed a large variance amongst individuals. In the suprahyoid muscles, the
2.3. Statistical analysis A distinction was made between pure fibre types that express one isoform and hybrid fibre types that express more than one isoform. For each muscle, the relative amount of the various pure and hybrid fibres was determined. To compare differences in fibre size, the cross-sectional area of these fibres was measured and related to their MyHC content. For each individual, the mean fibre-type distribution and cross-sectional area were calculated in the jaw closers and the suprahyoid and infrahyoid muscles. Then, the means of these three groups were calculated over all individuals. As the fibre-type distribution of the lateral pterygoid had more similarities with that of the jaw closers than with the jaw openers (Korfage and Van Eijden, 2000), we have included this muscle among the group of jaw closers. Differences in fibre-type distribution and in fibre crosssectional area of a particular MyHC isoform between muscle groups were analysed by the Wilcoxon signed ranking test for paired data. The level of significance was set to PB0.05.
3. Results The percentage of a particular fibre type did not differ significantly among the muscles of a particular group. The three muscle groups contained, on average, equal percentages of pure type I and type IIX fibres (Fig. 1). In contrast, the percentages of pure type IIA and hybrid fibres differed significantly between the jaw closers and the supra-/infrahyoid muscle groups. The supra- and infrahyoid muscles contained more type IIA fibres, whereas the jaw closers contained more hybrid fibres. In the three muscle groups, MyHC-fetal or cardiac-a were only found in hybrid fibres, in combination with one or more isoforms. Many different hybrid fibre
Fig. 1. Fibre-type composition (mean 9 S.D.) in human jaw closers, supra- and infrahyoid muscles. S.D. values are a measure of interindividual variability. MyHC, myosin heavy chain.
824
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
Fig. 2. Total proportion of fibres (mean 9 S.D.) expressing a given myosin heavy chain (MyHC) isoform in pure + hybrid fibres in jaw closers, supra- and infrahyoid muscles.
most abuntant hybrid fibre types were fibres expressing cardiac-a+IIA (2.0%), cardiac-a+I (1.5%), and I + IIA (1.3%), and in the infrahyoid muscles, fibres expressing cardiac-a+IIA (6.6%) and I +IIA (1.4%). The total amount of fibres (pure +hybrid) expressing a particular isoform showed that MyHC-I was expressed in about 70% of all fibres in the jaw closers, while this isoform was expressed in about 40% of all fibres in the suprahyoid muscles and in about 46% of all fibres in the infrahyoid muscles (Fig. 2). The supra-/ infrahyoid muscles contained significantly more fibres (about 50%) that expressed MyHC-IIA than the jaw closers (about 30%). Furthermore, jaw closers contained more fibres expressing MyHC-fetal or MyHCcardiac-a (10 and 25%, respectively) than the suprahyoid muscles (1 and 5%, respectively) and infrahyoid muscles (1 and 9%, respectively). These two isoforms showed a high interindividual variability. In the jaw-closing muscles, type I fibres were significantly larger (40%) than in the supra- and infrahyoid muscles (Fig. 3). No significant difference was seen in the cross-sectional area between other fibre types. Within the group of jaw closers, type I fibres were about 40% larger than other fibre types. This difference was not seen within the supra-/infrahyoid muscles.
4. Discussion This is, to the best of our knowledge, the first study to compare fibre-type distributions and cross-sectional areas amongst the jaw closers and the supra- and infrahyoid muscles in one group of human individuals. Within the groups, no large difference was seen in
fibre-type distribution or cross-sectional area (for jaw closers and openers, see Korfage et al., 2000). The fibre-type distributions and fibre cross-sectional areas of the human jaw muscles reported here and in other studies (Ringqvist, 1973; Vignon et al., 1980; Eriksson et al., 1982; Ringqvist et al., 1982; Eriksson and Thornell, 1983; Sciote et al., 1994; Uhlig et al., 1995; Monemi et al., 1999) are different from what is commonly found in limb and trunk muscles (Johnson et al., 1973; Polgar et al., 1973). Compared to those muscles, masticatory muscles have more hybrid fibres, many of them coexpressing MyHC-fetal and/or cardiac-a (Korfage and Van Eijden, 1999, 2000; Korfage et al., 2000). Furthermore, jaw muscle fibres have smaller cross-sectional areas. In human masticatory muscles, type I fibres are reportedly larger than type II fibres, while in limb and trunk muscles, the opposite is true (Ringqvist, 1974). However, the type I fibres in human jaw-closing muscle are not large in absolute terms; rather, the type II fibres are often unusually small. The present results indicate that these differences are more pronounced for jaw-closing than for supra- and infrahyoid muscles, as the supra-/infrahyoid muscles had fewer hybrid fibres than the jaw-closing muscles and type I fibres in the supra-/infrahyoids were not larger than type II fibres. Several explanations have been suggested for this difference between masticatory muscles and limb and trunk muscles, including differences in their function and/or nerve supply (Butler-Browne et al., 1988; Sta˚ l et al., 1994), differences in their genetic pathways for expressing muscle-specific proteins during embryogenesis, and differences in their chronological or spatial activation of some transcription factors (Marcucio and Noden, 1999).
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
The jaw closers and the supra-/infrahyoid muscles have different functions. In general, the jaw closers contract more slowly and experience more resistance during trituration of food than the supra- and infrahyoids. The jaw closers also exhibit continuous low-level electromyographic activity to maintain the mandibular rest position (Miller, 1991). In an earlier study, we demonstrated that jaw closers have architectural features that suit them to force production, whereas the suprahyoid muscles are better designed to produce larger excursions and larger velocities (Van Eijden et al., 1997). The present results indicate that such a specialization is reflected in the fibre-type composition of all three muscle groups. The jaw closers had more fibres expressing MyHC-I (pure +hybrid), whereas the supra- and infrahyoid muscles had more fibres expressing MyHC-IIA. Type I fibres, which express MyHC-I, contract more slowly than type II fibres, which express MyHC-IIA or IIX. Therefore, the jaw closers can be considered as slower than the supra-/infrahyoid muscles. According to the size principle (Henneman et al., 1965), type I motor units are recruited first in a motor task, whereas type II motor units are recruited when higher velocities or forces are required. The same recruitment order is applicable to human jaw muscles (Yemm, 1977; Scutter and Tu¨ rker, 1998). The jaw closers possess more fibres expressing MyHC-I, and the supra- and infrahyoid muscles possess more fibres expressing MyHC-II; this suggests that the jaw closers are more suited to displaying tonic activity, whereas the supra-/infrahyoid muscles are more suited to displaying phasic activity. Furthermore, type I motor units have
825
smaller innervation ratios than type II units (Burke and Tsairis, 1973). Therefore, it can be expected that the jaw closers will be better equipped to regulate the magnitude of the force produced during chewing or biting than the supra- and infrahyoid muscles. The exact proportion of individual MyHC isoforms within single hybrid fibres remains to be investigated. Another factor that might contribute to this better force-regulating capacity of the jaw closers is their higher proportion of hybrid fibres. Studies on the contractile properties of single muscle fibres and motor units expressing multiple MyHCs have shown that the coexpression of different MyHC isoforms yields a greater variance in shortening velocities and force generation than is possible in pure fibres (Johnson et al., 1994; Kwa et al., 1995; Sciote and Kentish, 1996). We also found that, in the jaw closers, the cross-sectional area of type I fibres was approx. 40% greater than in the supra-/infrahyoid muscles and that, in the jaw closers, type I fibres were larger than type II and hybrid fibres. The larger cross-sectional area of type I fibres compared to other fibre types confirms the findings of others (Ringqvist, 1974; Vignon et al., 1980; Eriksson and Thornell, 1983). These larger cross-sectional areas might be the result of the larger resistance experienced by the jaw closers during chewing. Training against resistance causes an increase in fibre cross-sectional area (McCall et al., 1996), while weightlessness causes a decrease (Edgerton et al., 1995). As we used material from elderly individuals, which might not have the same phenotype as young adults, we have compared our data with those from other studies in which masticatory muscles of either young or old
Fig. 3. Fibre-type cross-sectional area (mean 9 S.D.) of the jaw closers, supra- and infrahyoid muscles. S.D. values are a measure for interindividual variability. MyHC, myosin heavy chain.
826
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827
individuals were examined. From this comparison, it appears that young individuals have more type I and fewer hybrid fibres than elderly individuals, suggesting that the proportion of type I fibres decreases, and that of hybrid fibres increases with age (Vignon et al., 1980; Eriksson and Thornell, 1983; Monemi et al., 1999; Korfage et al., 2000). The variability in fibre-type proportion and cross-sectional area was relatively large. Possible explanations are (1) the samples were drawn from heterogeneous populations; (2) differences in facial morphology; (3) difference in the usage of the muscles; (4) difference in the age of the individuals. Acknowledgements This research was supported institutionally by the Interuniversitary Research School of Dentistry, through the Academic Centre of Dentistry Amsterdam. We would like to express our gratitude to L.J. van Ruijven for the technical support and J. Ruijter for statistical advice. References Bottinelli, R., Caneparri, M., Pellegrino, M.A., Reggiani, C., 1996. Force – velocity properties of human skeletal muscle fibres: myosin heavy chain isoforms and temperature dependence. J. Physiol. 495, 573 –586. Bredman, J.J., Wessels, A., Weijs, W.A., Korfage, J.A.M., Soffers, C.A.S., Moorman, A.F.M., 1991. Demonstation of ‘cardiac-specific’ myosin heavy chain in masticatory muscles of human and rabbit. Histochem. J. 23, 160 –170. Burke, R.E., Tsairis, P., 1973. Anatomy and innervation ratios in motor units of cat gastrocnemius. J. Physiol. 234, 749 – 765. Butler-Browne, G.S., Eriksson, P.-O., Laurent, C., Thornell, L.-E., 1988. Adult human masseter muscle fibres express myosin isozymes characteristic of development. Muscle and Nerve 11, 610 – 620. Edgerton, V.R., Zhou, M.-Y., Ohira, Y., Klitgaard, H., Jiang, B., Bell, G., Harris, B., Saltin, B., Gollnick, P.D., Roy, R.R., Day, M.K., Greenisen, M., 1995. Human fiber size and enzymatic properties after 5 and 11 days of spaceflight. J. Appl. Physiol. 78, 1733 –1739. Eriksson, P.-O., Eriksson, A., Ringqvist, M., Thornell, L.-E., 1982. Histochemical fibre composition of the human digastric muscle. Arch. Oral Biol. 27, 207 –215. Eriksson, P.-O., Thornell, L.-E., 1983. Histochemical and morphological muscle-fibre characteristics of the human masseter, the medial pterygoid and the temporal muscle. Arch. Oral Biol. 28, 781 –795. Henneman, E., Somjen, G., Carpenter, D.O., 1965. Functional significance of cell size in spinal motoneurons. J. Neurophysiol. 28, 560 – 580. Johnson, M.A., Polgar, J., Weightman, D., Appleton, D., 1973. Data on the distribution of fibre types in thirty-six human muscles. An autopsy study. J. Neurol. Sci. 18, 111 – 129.
Johnson, B.D., Wilson, L.E., Zhan, W.Z., Watchko, J.F., Daood, M.J., Sieck, G.C., 1994. Contractile properties of the developing diaphragm correlate with myosin heavy chain phenotype. J. Appl. Physiol. 77, 481 – 487. Korfage, J.A.M., Van Eijden, T.M.G.J., 1999. Regional differences in fibre type composition in the human temporalis muscle. J. Anat. 194, 355 – 362. Korfage J.A.M., Van Eijden T.M.G.J., 2000. Myosin isoform composition of the human medial and lateral pterygoid muscles. J. Dent. Res, 79, 1618 – 1625. Korfage J.A.M., Brugman P., Van Eijden T.M.G.J., 2000. Intermuscular and intramuscular differences in myosin heavy chain composition of the human masticatory muscles. J. Neurol. Sci, 178, 95 – 106. Kwa, S.H.S., Weijs, W.A., Ju¨ gh, P.J.W., 1995. Contraction characteristics and myosin heavy chain composition of rabbit masseter motor units. J. Neurophysiol. 73, 538 – 549. Lieber, R.L., Blevins, F.T., 1989. Skeletal muscle architecture of the rabbit hindlimb: functional implications of muscle design. J. Morphol. 199, 93 – 101. McCall, G.E., Byrnes, W.C., Dickinson, A., Pattany, P.M., Fleck, S.J., 1996. Muscle fiber hypertrophy, hyperplasia, and capillary density in college men after resistance training. J. Appl. Physiol. 81, 2004 – 2012. Marcucio, R.S., Noden, D.M., 1999. Myotube heterogeneity in developing chick craniofacial skeletal muscles. Dev. Dynam. 214, 178 – 194. Miller, A.J., 1991. Craniomandibular Muscles: Their Role in Function and Form. CRC Press, Boca Raton, FL. Monemi, M., Eriksson, P.-O., Kadi, F., Butler-Browne, G.S., Thornell, L.-E., 1999. Opposite changes in myosin heavy chain composition of human masseter and biceps brachii muscles during aging. J. Muscle Res. Cell Motil. 20, 351 – 361. Pette, D., Staron, R.S., 1990. Cellular and molecular diversities of mammalian skeletal muscle fibres. Rev. Physiol. Biochem. Pharmacol. 116, 2 – 76. Polgar, J., Johnson, M.A., Weightman, D., Appleton, D., 1973. Data on fibre size in thirty-six human muscles. An autopsy study. J. Neurol. Sci. 19, 307 – 318. Ringqvist, M., 1973. Fibre sizes of human masseter muscle in relation to bite force. J. Neurol. Sci. 19, 297 – 305. Ringqvist, M., 1974. Fiber types in human masticatory muscles. Relation to function. Scand. J. Dent. Res. 82, 333 – 355. Ringqvist, M., Ringqvist, I., Eriksson, P.-O., Thornell, L.-E., 1982. Histochemical fibre-type profile in the human masseter muscle. J. Neurol. Sci. 53, 273 – 282. Sant’Ana Pereira, J.A.A., Wessels, A., Nijtmans, L., Moorman, A.F.M., Sargeant, A.J., 1995. New method for the accurate characterization of single human skeletal muscle fibres demonstrates a relation between mATPase and MyHC expression in pure and hybrid fibre types. J. Muscle Res. Cell Motil. 16, 21 – 34. Schiaffino, S., Reggiani, C., 1994. Myosin isoforms in mammalian skeletal muscle. J. Appl. Physiol. 77, 493 – 501. Sciote, J.J., Rowlerson, A.M., Hopper, C., Hunt, N.P., 1994. Fibre type classification and myosin isoforms in the human masseter muscle. J. Neurol. Sci. 126, 15 – 24. Sciote, J.J., Kentish, J.C., 1996. Unloading shortening velocities of rabbit masseter muscle fibres expressing skeletal or a-cardiac myosin heavy chains. J. Physiol. 492, 659 – 667.
J.A.M. Korfage et al. / Archi6es of Oral Biology 46 (2001) 821–827 Scutter, S.D., Tu¨ rker, K.S., 1998. Recruitment stability in masseter motor units during isometric voluntary contractions. Muscle and Nerve 21, 1290 –1298. Sta˚ l, P., Eriksson, P.-O., Schiaffino, S., Butler-Browne, G.S., Thornell, L.-E., 1994. Differences in myosin composition between human oro-facial, masticatory, and limb muscles: enzyme-, immunohisto- and biochemical studies. J. Muscle Res. Cell Motil. 15, 517 – 534. Uhlig, Y., Weber, B.R., Grob, D., Muntener, M., 1995. Fiber composition and fiber transformations in neck muscles of patients with dysfunction of the cervical spine. J. Orthopaed. Res. 13, 240 – 249. Van Eijden, T.M.G.J., Korfage, J.A.M., Brugman, P., 1997. Architecture of the human jaw-closing and jaw-opening muscles. Anat. Rec. 248, 464 –474. Vignon, C., Pellissier, J.F., Serratrice, G., 1980. Further histochemical studies on masticatory muscles. J. Neurol. Sci. 45, 157 – 176.
.
827
Weiss, A., Schiaffino, S., Leinwand, L.A., 1999. Comparative sequence analysis of the complete human sarcomeric myosin heavy chain family: implications for functional diversity. J. Mol. Biol. 290, 61 – 75. Wessels, A., Vermeulen, J.L.M., Viragh, Sz., Ka´ lma´ n, F., Lamers, W.H., Moorman, A.F.M., 1991. Spatial distribution of ‘tissue specific’ antigens in the developing human heart and skeletal muscle. II. An immunohistochemical analysis of myosin heavy chain isoform expression patterns in the embryonic heart. Anat. Rec. 229, 355 – 368. Wickiewicz, T.L., Roy, R.R., Powell, P.L., Edgerton, V.R., 1983. Muscle architecture of the human lower limb. Clin. Orthopaed. Relat. Res. 179, 275 – 283. Yemm, R., 1977. The orderly recruitment of motor units of the masseter and temporal muscles during voluntary isometric contraction in man. J. Physiol. 265, 163 – 174.