Effects of Various Ions on the Resting and Active Membrane of the Somatic Muscle of the Earthworm

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Abstract
The properties of the membrane, in both the resting and the active state, of the longitudinal muscle of the earthworm were studied under various ionic environments. The maximum slope of the membrane potential change against a tenfold change in the external potassium concentration was 27 mV. in the presence of external sodium and 42 mV. in the absence of external sodium. In the normal external potassium concentration the removal of sodium hyperpolarized the membrane from a normal resting potential of – 36 to – 58 mV. Reduction of the external calcium concentration to a tenth of its normal value depolarized the membrane by about 16 mV. In excess of external potassium the spike height and the after-hyperpolarization were decreased and the duration of the spike was prolonged. In sodium-free solution spikes with an overshoot potential were generated both spontaneously and under the stimulus of an intracellularly depolarizing current. The amplitude and the maximum rate of rise of the spike were dependent on the external calcium concentration, whether or not sodium was present externally. Manganese modified the membrane activity by competition with calcium.