Abstract
1) The effects of adrenaline, ouabain, low-K Ringer, and low-Na Ringer on the time course of twitch contraction were studied in the ventricular preparations of bullfrog, with special reference to their effects on relaxation.
2) Adrenaline (10-7-10-6 g/ml) had the effect of enhancing the relaxation of twitch, in addition to its potentiating effect.
3) Ouabain (10-7-10-6 M) only potentiated the twitch without an appreciable effect on the relaxation phase.
4) Low-K Ringer (0.16 mm-K), as well as low-Na Ringer (50 %-Na), reduced the rate of relaxation of twitch.
5) Low-Na Ringer had an additional effect to shorten the time to maximum rate of rise of tension.
6) These effects were evaluated quantitatively by an analysis in which the increase in the rate of fall of tension was compared with the increase in peak tension or with the increase in the rate of rise of tension.
7) Possible subcellular mechanisms to explain the results were discussed.
