The effect of temperature on the contraction characteristics of jaw muscles in the cat

Archs oral Biol. Vol. 29, No. 6, pp. 477478,

0003-9969/84 $3.00 + 0.00

1984

Copyright 0 1984 Pergamon Press Ltd

Printed in Great Britain. All rights reserved

SHORT COMMUNICATION THE EFFECT OF TEMPERATURE ON THE CONTRACTION CHARACTERISTICS OF JAW MUSCLES IN THE CAT K. S. T~~RKER* and B. R. MACKENNA Institute of Physiology, Glasgow University, Glasgow G12 SQQ, Scotland, U.K. Summary-The effect of muscle temperature on the speed of contraction and on the strength of contraction of the cat jay muscles was studied. Muscles contracted faster when their temperatures were increased. The tetanic and twitch tension decreased significantly as the animal was heated from 30 to 40°C.

In previous studies on jaw-muscle contraction, the temperature of the muscle under investigation either was not reported (Tamari er al., 1973) or various muscle temperatures were used; 35°C (Hiraiwa, 1978), 37-38°C (Taylor, Cody and Bosley, 1973). As It is well known that muscle temperature affects the speed and strength of contraction (Butler, Ranatunga and Smith, 1968; Close and Hoh, 1968), this point was considered to be worth further study. Twelve anaesthetized (Nembutal), decerebrated (trigeminal nerves also cut) cats were used. The body (and thus muscle) temperature was lowered using plastic bags containing ice cubes. Once the lowest stable temperature was reached, about 28-3 1“C (rectal) the animal was gradually heated using an electric blanket at a rate of 2°C per hour. The jaws were fixed in mid-open position (15 mm between incisors). For each degree of temperature increase, twitch and *Present address: Department of Physiology, The University of Adelaide, G.P.O. Box 498, Adelaide 5001, South Australia.

tetanic tensions were recorded using a storage oscilloscope. Time-to-peak twitch tension as well as the contraction strength of the twitch and tetanic tension were noted. The jaw muscles were either stimulated via their nerves (masseter) or stimulated using bipolar wire electrodes. The method used for holding the cat’s head and recording the contraction of the jaw muscles has been reported (Mackenna and Tiirker, 1977, 1978). The effect of temperature on the contraction speed of several jaw muscles of the cat is shown in Fig. l(a). When the muscle temperature of the animal was allowed to rise, the time-to-peak (TTP) value decreased (the muscle contracted faster). When the rectal temperature was 27S”C, TTP was 40ms. As the temperature was increased, there was a gradual drop in the TTP. At 39”C, rectal TTP was 20 ms (50 per cent reduction). The effect of muscle temperature on the strength of the twitch and tetanic tension was as follows: the twitch and tetanic tension decreased as the tem-

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K. S. T~~RKERand B. R. MACKENNA

Muscle temperature (%I FIG. I(b) Fig. I. (a) The effect of temperature on the time-to-peak contraction of various jaw muscles. Note the difference between the rectal and muscle temperature. (b) The effect of temperature on the twitch and tetanic tensions of the masseter muscle of anaesthetized, decerebrated cats. Twitch and tetanic tensions at 31°C (rectal) were taken as 100 per cent; the tensions recorded at other temperatures are shown as a percentage of this.

perature of the animal was increased; the decrease in twitch tension was approx. 50 per cent and in tetanic tension approx. 30 per cent (Fig. 1b). The jaw-muscle temperature of the animal was always 3-3S”C lower than the rectal temperature. Our findings on the speed of contraction agree with all previous work in this field (Maclagan and Zaimis, 1957; Close and Hoh, 1968; Buller et al., 1968). An increase in muscle temperature always causes a decrease in TTP. Our findings on the changes of the twitch and tetanic tension with muscle temperature agree with those of Maclagan and Zaimis (1957) who worked on the tibialis anterior muscle of the cat. Our findings might explain why the values of the TTP of jaw muscles were found to be different by different workers. Muscle temperature is an important variable in studying the contraction characteristics of jaw muscles. REFERENCES

Buller A. J., Ranatunga K. W. and Smith J. M. (1968) The influence of temperature on the contractile characteristics

of mammalian fast and slow twitch skeletal muscles. J. Physiol. I%, 82~. Close R. and Hoh J. F. Y. (1968) Influences of temperature

on isometric contractions of rat skeletal muscles. Nature 217, 1179-l 180. Hiraiwa T. (1978) Histochemical properties of masticatory muscles of growing rat and matured mammals. Camp. Biochem. Physiol. 59a, 23 l-238. Mackenna B. R. and Tiirker K. S. (1977) A method for studying the length-tension relationships of the jaw muscles of the cat. 7. Physiol. 273, 21-22P. Mackenna B. R. and Tiirker K. S. (1978) Twitch tension in the jaw muscles of the cat at various’degrees of mouth opening. Archs oral Biol. 23, 917-920. Maclagan J. and Zaimis E. (1957) The influence of muscle

temperature on twitch and tetanus in the cat. J. Phvsiol. 137; 89-90P. Tamari J. W.. Tomev G. F.. Ibrahim M. Z. M.. Bakara A.. Jabbur S. J: and Batuth N. (1973) Correlative’study of the physiologic and morphologic characteristics of the temporal and masseter muscles of the cat. J. dent. Res. 52, 538-543.

Taylor A., Cody F. W. J. and Bosley M. A. (1973) Histochemical and mechanical properties of the jaw muscles of the cat. Expl Neurof. 38, 99-109.