IONIC BASES OF SLOW, DEPOLARIZING RESPONSES OF CARDIAC GANGLION NEURONS IN THE CRAB, PORTUNUS-SANGUINOLENTUS

A feature of intracellular recordings from neurons of the cardiac ganglia of stomatopods and several species of crabs and lobsters is the presence of a sustained depolarization underlying the rhythmically recurring burst of synaptic potentials and electrotonically decremented impulses. The preceding paper presented observations of a slow, active, depolarizing response that could be elicited by depolarizing current when all other electrical activity had been inhibited by continuous perfusion of the preparation with tetrodotoxin (TTX). Changes of these responses to various perturbations of membrane potential provided evidence constistent with the suggestion that these responses, termed driver potentials, represented the slow potentials seen to underlie spontaneous burst activity and are the source of current for generation of impulse bursts. The observation of marked increases in conductance during driver potentials suggests their generation by ionic currents. This paper presents the results of experiments to explore the participation of calcium, sodium, and potassium ions in the generation of driver potentials.