SYNAPTIC ACTIVATION OF AN ELECTROGENIC SODIUM PUMP

An identified molluscan interneuron mediates different cholinergic synoptic actions by increasing the conductance of its follower cells to different ions. We have now found that this interneuron also mediates a new class of synoptic actions which does not involve a conductance change but the activation of an electrogenic sodium pump. This synoptic action results in a prolonged inhibitory synoptic potential which is dependent on metabolism and is selectively blocked by cooling and ouabain. In cells which have this synoptic potential, part of the resting membrane potential is also maintained by an electrogenic sodium pump. The same transmitter, acetylcholine, can independently stimulate both a chloride ion conductance and a sodium pump mechanism in the same follower cell by acting on two different postsynaptic receptors.