[Ionic mechanisms of the excitatory action of transmitter, exogenous acetylcholine and serotonin on neurons of the superior cervical ganglion in rabbits].

Ionic mechanisms of EPSP and depolarization evoked by iontophoretically applied acetylcholine (Ach) and serotonin (5-hydroxytryptamine, 5-HT) in the neurons of the rabbit isolated superior cervical ganglion (ACh-potential and 5-HT-potential, respectively) were studied using intracellular electrodes. Reversal potentials of EPSP (EEPSP) and Ach-potential (EACh) were -14.4 +/- 1.6 mV and -16.5 +/- 1.2 mV, for 5-HT-potential they were close to these values. More negative values of EEPSP and EACh were obtained in a group of neurons (about 1/3) using the extrapolation method, probably due to an increase in their membrane resistance during hyperpolarization. A decrease in external sodium or potassium concentration made EEPSP and EACh more negative, and an increase in external potassium concentration made them more positive than in normal solution. Changes in external chloride concentration do not influence EEPSP and EACh. It is concluded that excitatory transmitter and exogenous ACh (as well as probably 5-HT) increase membrane permeabilities to sodium and potassium ions.