Separation of tubular electrical activity in amphibian skeletal muscle through temperature change

The effect of temperature on the form of the propagated action potential was investigated in frog skeletal muscle fibres. Increasing the temperature decreased the duration of the initial overshoot but a hump then appeared during a more prominent after-depolarization. Finally, at 28-30 degrees C, the after-depolarization was either noticeably enlarged or entirely absent. This all-or-none failure of tubular conduction suggests that excitation of the tubular membrane takes place through regenerative activity rather than graded electrotonic spread of depolarization. However, it is consistent with a partial electrical isolation of the tubular lumina, possibly through the access resistance proposed in earlier theoretical models for muscle membrane.