抄録
1. When the double indirect stimuli more than 70 msec. apart were applied to the partially curarized frog muscle, the second action potential of the muscle was smaller than the first one and the depression lasted more than 10 sec. The depression was also observed in the twitch height of the uncurarized gastrocnemiusmuscle in vivo.
2. The magnitude of depression of e.p.p. after a conditioning stimulus was about 10-15 per cent and its time course was quite similar to that of the partially curarized muscle action potential.
3. The time course of depression of e.p.p. was exponential and its time constant was 4-5 sec. at 25°C.
4. Lowering the temperature decreased the magnitude of depression and lengthened the time course. Q10was about 1.7 in the range of temperature 15-25°C.
5. Calcium deficiency and an addition of magnesium to Ringer's solution decreased the size of depression. In calcium rich solution the size of depression augmented but its time course was the same. Potassium and eserine had little or no effect on the magnitude and time course of depression.
6. The lengthening of muscle increased the depression.
7. The increase in number of conditioning stimuli augmented the depression but had little effect on its time course.
8. Repetitive stimulation of low frequency caused the decline of the amplitude of successive e.p.p.'s, and the rate of decrease was much more slower after five or six responses.
