Depolarization of electroplax membrane in calcium-free ringer's solution

Electrical stimulation, either cathodal or anodal, of the monocellular electroplax preparation in Ca-free Ringer's solution results in a sustained depolarization which is determined by the amount of current passed through the cell. The membrane potential recovers only when Ca is added again. These changes take place at the innervated side of the electroplax only. This depolarization of the membrane is pH-dependent; it depolarizes more at pH 6.0 than at pH 9.0. The membrane does not depolarize and the action potential is not blocked within an hour in Ca-free solution unless the cell is stimulated. The sustained depolarization is not prevented or reversed by curare, tetracaine, physostigmine, tetrodotoxin, and tetraethylammonium.After stimulation, the outward K current remains unchanged regardless of whether Ca is present. In contrast, the inward current is dependent on Ca in the outside solution on the innervated membrane; in the absence of Ca following stimulation, the inward K current is decreased.The depolarization by carbamylcholine is reduced in Ca-free and increased in Mgfree Ringer's solution. In contrast to the depolarization induced by electrical stimulation, these carbamylcholine depolarizations may be reversed by washing with Ca-free or Ca- and Mg-free Ringer's solution.