- Email: [email protected]
Symposium: Control Mechanisms of Biodynamic Phenomena Chair: A. Matsuno (Shimane), Organizer: T. Tsuchiya (Kobe)
Comparative Biochemistry and Physiology, Part B 139 (2004) 769 – 770 www.elsevier.com/locate/cbpb
Symposium: Control Mechanisms of Biodynamic Phenomena Chair: A. Matsuno (Shimane), Organizer: T. Tsuchiya (Kobe) SA1 Physiology of Amoeba proteus: ameboid movement and contractile vacuole Seiji Sonobe, Grad. Sch. Life Sci., University of Hyogo, Hyogo 678-1297, Japan A large free-living amoeba, Amoeba proteus, is a good material for physiological and even biochemical studies. Our interest focuses on how the cell harmonize various cell functions in the cell which has no differentiated organelles and structures which determine cell polarity like as microtubules. In this symposium, I would like to talk about a part of our works on amoeboid movement and contractile vacuole (CV). We have studied on the molecular mechanism of ameboid movement using model system and biochemical technique and elucidated that actin phosphorylation plays an important role in actin dynamics, and Ca and phospholipids are involved in association of actin filaments with the plasma membrane. Contractile vacuole is an organelle characteristic to unicellular organism living in fresh water and functions in water excretion. Electron microscopy revealed that CV are surrounded by many small vesicles with a diameter of approx. 0.1 Am. Shrinkage of an isolated CV from burst amoeba induced by high osmorality solution and expansion by subsequent low osmorality solution indicated semi-permeability of CV membrane. I would like to discuss on the future works to solve the mechanism of water accumulation and expulsion of CV. SA2 Regulation of motile activities by various factors in fish chromatophores Noriko Oshima, Dept. Biomolec. Sic., Fac. Sci., Toho University, Funabashi 274–8510, Japan Many of fish chromatophores possess cellular motility, by which fishes can change their skin colors and patterns. Chromatophores are under the control of sympathetic nervous and endocrine systems. Norepinephrine induces pigment aggregation in melanophores, erythrophoers and xanthophores, and the transmission is alpha–adrenergic in nature, but pigment dispersion is caused via beta-adrenergic receptors in leucophores. Adenosine released from nerve fibers along with norepinephrine induces pigment dispersion mediated through adenosine receptors. Alpha-MSH disperses pigment granules, and MCH is generally antagonistic to MSH. These hormones also affect chromatophores directly through their specific receptors. Melatonin elicits pigment aggregation or dispersion through alpha- or beta-receptors, respectively. Prolactin causes pigment dispersion only in erythrophores and xanthophores. Recently, endothelins were also found to induce pigment migration and coloring response in lightabsorbing chromatophores and iridophores, respectively, via ETB-receptors. In addition, light-sensitive chromatophores that respond directly to doi:10.1016/j.cbpc.2004.09.003
light have been found in some adult fish species. We found the expression of opsin mRNAs in the skin of some fishes, where the light-sensitive chromatophores exist. In any case, cAMP or Ca2+ may be involved in the signal transduction. SA3 Dynamic properties of muscle contraction in situ—studies on human movements with slack-test and force-clamp method Naokata Ishii, Dept. Life Sci., Grad. Sch. Arts Sci., University of Tokyo, Tokyo 153–8902, Japan A number of studies have so far shown a common, hyperbolic nature of the force–velocity relations in various stages of animal movements, i.e. sliding between actin and myosin, and contractions of single fibers and isolated muscles. However, contractile properties of muscle in real movements of organisms remain unclear because of the presence of complex nervous control. In addition, the movements are likely produced by coordinated contractions of many muscles around more than one joint. To solve these problems, precise measurements of movement velocities under steady state condition would be required. For this purpose, we have developed novel techniques for applying the slack-test (Edman, 1978) and force-clamp methods to human movements. The slack-test was applied to plantar flexor muscles to measure their unloaded velocity (V 0) under varied activation levels (10–60% of maximal voluntary force). Against the prediction by the bsize principleQ for motor unit recruitment, V 0 did not show a significant dependence on the activation level. The force-clamp was applied to multijoint, knee-hip extension movements, and showed that the force–velocity relations are well described by a linear function rather than a hyperbola. The mechanism underlying this phenomenon was interpreted in terms of the changes in muscle activation level with force. SA4 Motility and body support by mechanically active connective tissues Tatsuo Motokawa, Dept. Biol. Sci., Grad. Sch. Biosci. Biotechnol., Tokyo Institute Technol., Tokyo 152–8551, Japan Mechanically active connective tissues of echinoderms are reviewed. We recently found the contraction in the ligaments connecting ossicles of crinoids (Motokawa et al., Biol. Bull. 206:4–12, 2004). They are made of bundles that consist mainly of striated collagenous fibrils and interspersed microfibrils, possibly made of some elastic protein. The cells with secretory granules, whose cell bodies are found inside the ossicles, send processes into the ligament. There are no muscle cells in the ligament, and yet it contracts in response to acetylcholine. The ligament exerted a force under isometric condition and shortened under isotonic condition. We coined the
770
Abstracts
word bcontractile connective tissueQ to this ligament. Another example of mechanically active connective tissues of echinoderms is the catch connective tissue (mutable connective tissue). The catch connective tissue changes its mechanical properties rapidly and reversibly under nervous control. The merit to have catch connective tissues is in economy: it
maintains body posture with as little energy as 1/10 that of muscles. The main component of the catch connective tissue is extracellular materials such as collagen and proteoglycans. The ease of slippage of collagen fibrils seems to be modulated by proteins secreted from neurosecretory cells under nervous control.
Symposium: Control Mechanisms of Biodynamic Phenomena Chair: A. Matsuno (Shimane), Organizer: T. Tsuchiya (Kobe) SA1 Physiology of Amoeba proteus: ameboid movement and contractile vacuole Seiji Sonobe, Grad. Sch. Life Sci., University of Hyogo, Hyogo 678-1297, Japan A large free-living amoeba, Amoeba proteus, is a good material for physiological and even biochemical studies. Our interest focuses on how the cell harmonize various cell functions in the cell which has no differentiated organelles and structures which determine cell polarity like as microtubules. In this symposium, I would like to talk about a part of our works on amoeboid movement and contractile vacuole (CV). We have studied on the molecular mechanism of ameboid movement using model system and biochemical technique and elucidated that actin phosphorylation plays an important role in actin dynamics, and Ca and phospholipids are involved in association of actin filaments with the plasma membrane. Contractile vacuole is an organelle characteristic to unicellular organism living in fresh water and functions in water excretion. Electron microscopy revealed that CV are surrounded by many small vesicles with a diameter of approx. 0.1 Am. Shrinkage of an isolated CV from burst amoeba induced by high osmorality solution and expansion by subsequent low osmorality solution indicated semi-permeability of CV membrane. I would like to discuss on the future works to solve the mechanism of water accumulation and expulsion of CV. SA2 Regulation of motile activities by various factors in fish chromatophores Noriko Oshima, Dept. Biomolec. Sic., Fac. Sci., Toho University, Funabashi 274–8510, Japan Many of fish chromatophores possess cellular motility, by which fishes can change their skin colors and patterns. Chromatophores are under the control of sympathetic nervous and endocrine systems. Norepinephrine induces pigment aggregation in melanophores, erythrophoers and xanthophores, and the transmission is alpha–adrenergic in nature, but pigment dispersion is caused via beta-adrenergic receptors in leucophores. Adenosine released from nerve fibers along with norepinephrine induces pigment dispersion mediated through adenosine receptors. Alpha-MSH disperses pigment granules, and MCH is generally antagonistic to MSH. These hormones also affect chromatophores directly through their specific receptors. Melatonin elicits pigment aggregation or dispersion through alpha- or beta-receptors, respectively. Prolactin causes pigment dispersion only in erythrophores and xanthophores. Recently, endothelins were also found to induce pigment migration and coloring response in lightabsorbing chromatophores and iridophores, respectively, via ETB-receptors. In addition, light-sensitive chromatophores that respond directly to doi:10.1016/j.cbpc.2004.09.003
light have been found in some adult fish species. We found the expression of opsin mRNAs in the skin of some fishes, where the light-sensitive chromatophores exist. In any case, cAMP or Ca2+ may be involved in the signal transduction. SA3 Dynamic properties of muscle contraction in situ—studies on human movements with slack-test and force-clamp method Naokata Ishii, Dept. Life Sci., Grad. Sch. Arts Sci., University of Tokyo, Tokyo 153–8902, Japan A number of studies have so far shown a common, hyperbolic nature of the force–velocity relations in various stages of animal movements, i.e. sliding between actin and myosin, and contractions of single fibers and isolated muscles. However, contractile properties of muscle in real movements of organisms remain unclear because of the presence of complex nervous control. In addition, the movements are likely produced by coordinated contractions of many muscles around more than one joint. To solve these problems, precise measurements of movement velocities under steady state condition would be required. For this purpose, we have developed novel techniques for applying the slack-test (Edman, 1978) and force-clamp methods to human movements. The slack-test was applied to plantar flexor muscles to measure their unloaded velocity (V 0) under varied activation levels (10–60% of maximal voluntary force). Against the prediction by the bsize principleQ for motor unit recruitment, V 0 did not show a significant dependence on the activation level. The force-clamp was applied to multijoint, knee-hip extension movements, and showed that the force–velocity relations are well described by a linear function rather than a hyperbola. The mechanism underlying this phenomenon was interpreted in terms of the changes in muscle activation level with force. SA4 Motility and body support by mechanically active connective tissues Tatsuo Motokawa, Dept. Biol. Sci., Grad. Sch. Biosci. Biotechnol., Tokyo Institute Technol., Tokyo 152–8551, Japan Mechanically active connective tissues of echinoderms are reviewed. We recently found the contraction in the ligaments connecting ossicles of crinoids (Motokawa et al., Biol. Bull. 206:4–12, 2004). They are made of bundles that consist mainly of striated collagenous fibrils and interspersed microfibrils, possibly made of some elastic protein. The cells with secretory granules, whose cell bodies are found inside the ossicles, send processes into the ligament. There are no muscle cells in the ligament, and yet it contracts in response to acetylcholine. The ligament exerted a force under isometric condition and shortened under isotonic condition. We coined the
770
Abstracts
word bcontractile connective tissueQ to this ligament. Another example of mechanically active connective tissues of echinoderms is the catch connective tissue (mutable connective tissue). The catch connective tissue changes its mechanical properties rapidly and reversibly under nervous control. The merit to have catch connective tissues is in economy: it
maintains body posture with as little energy as 1/10 that of muscles. The main component of the catch connective tissue is extracellular materials such as collagen and proteoglycans. The ease of slippage of collagen fibrils seems to be modulated by proteins secreted from neurosecretory cells under nervous control.