Abstract
Ionic mechanisms of EPSP generation and depolarization induced by iontophoretic application of acetylcholine (ACh) and serotonin (5-hydroxytryptamine, 5-HT) — acetylcholine and serotonin potentials — were investigated in neurons of the isolated rabbit superior cervical ganglion by means of intracellular microelectrodes. The reversal potentials (Er) for EPSP and the ACh-potential were −14.4±1.6 and −16.5±1.2 mV respectively, and they were about the same for the 5-HT potential. In some neurons (about one-third) much more negative values for Er were obtained for EPSP and the ACh-potential by extrapolation, probably due to an increase in the resistance of their membrane during hyperpolarization. A decrease in the external sodium and potassium concentrations was shown to make Er for EPSP and the ACh-potential more negative, whereas an increase in the external potassium concentration made it more positive than in normal solution; a change in the external chloride concentration did not alter Er. It is suggested that the excitatory transmitter and exogenous ACh (and also, probably, 5-HT) share the same ionic mechanism of action of the membrane, which includes an increase in the permeability of the membrane to two ions — sodium and potassium — simultaneously.
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