Abstract
Electrical and mechanical properties of M. digastricus of the guinea pig were investigated by the microelectrode and strain gauge methods.
1) The mean diameter of the musclefibres was 45.9μ. The triad structures appeared in the region of the A-I junction, i. e. two triad structures appeared within one sarcomere.
2) The resting membrane potential was-81.9mV. One type of muscle fiber had a length constant 0.72 mm, specific membrane resistance 1, 300Ωcm2, internal resistance of the muscle 290Ωcm, whereas the other type of muscle fiber gave values of 0.72mm, 330Ωcm2 and 73Ωcm respectively.
3) The changes of the membrane potential in various external concentrations of K ion were observed. The maximum slope of membrane potential change for tenfold change of K ion was 54 mV in solutions prepared so that [K] o×[Cl] o=constant.
4) Spikes could be elicited by electrical stimulation. The overshoot was 15 mV and the maximum rates of rise and fall were 340V/sec and 134 V/sec respectively.
5) The conduction velocity of excitation was 2.9m/sec, the time constant of foot of the propagated spike was 0.1 msec and the chronaxie was 0.39 msec.
6) The time constant of the membrane was calculated by various methods based on the cable theory, and the calculated values of the time constant were discussed in terms of the activity and structure of the muscle.
7) Although two types of the muscle fibre were distinguishable from their electrical properties, these two types could not be classified, from the results of this study, into fast and slow (or twitch and tonic) muscles.
8) Electrical stimulation and excess K ion evoked tension development, the threshold potential necessary to produce tension development being-35mV.
9) Caffeine and thymol modified the mechanical responses of the muscle. Caffeine enhanced the amplitude and prolonged the time taken to reach the peak of the contraction. Thymol, on the other hand, prolonged the relaxation time. Presumably caffeine increased the release of Ca ion and thymol inhibited the reabsorption of Ca ion by the reticulum.
10) The mechanical responses of M. digastricus were compared with those of M. semitendinosus.
