抄録
Histochemical and physiological properties of M. digastricus and M. semitendinosus of the guinea pig were investigated and compared since both muscle tissues have a red colour.
1) Action potential (overshoot potential; 14.9 mV) and membrane potential (-82.4 mV) recorded for M. digastricus were nearly the same as those obtained for M. semitendinosus (11.0 mV and -81.5 mV, respectively).
2) Both muscles generated twitch tension upon electrical stimulation; duration of tension was, however, much shorter in M. digastricus (42 msec at 35°C) than in M. semitendinosus (280 msec at 35°C). Active state of the mechanical response measured by the quick-release method also elucidated similar properties.
3) In the presence of various foreign anions (Br-, NO3- and SCN-), mechanical response of M. digastricus and M. semitendinosus were potentiated without any change of the membrane potential.
4) The critical membrane potentials for triggering K-induced contracture were -42 mV (70. 3mM K) in M. digastricus and -64 mV (26.7 mM K) in M. semitendinosus. These critical membrane potentials were lowered in Br-- and NO3-- Krebs solutions.
5) In both muscles the maximum slopes of the membrane depolarization produced by tenfold changes of [K]0 in various anions (NO3- and Br-) were the same as those observed in the presence of Cl-, but the slope became steeper in the presence of SCN-.
6) In M. digastricus, caffeine (1-5 mM) potentiated twitch tension. In a 20 mM concentration of caffeine, contracture was produced. A 0.5 mM concentration of thymol potentiated the mechanical response, produced contracture and depolarized the membrane. In M. semitendinosus, caffeine showed more marked effects than those observed in M. digastricus.
