Electrogenesis of the slow inhibitory postsynaptic potential in bullfrog sympathetic ganglia.

Abstract

The ionic mechanisms of the slow surface positive (P)-potential and the slow inhibitory postsynaptic potential (IPSP), an intracellularly recorded P-potential in sympathetic ganglia, were analyzed by means of sucrosegap, intracellular microelectrode techniques and voltage clamp technique. Both the P-potential and the slow IPSP consist of 2 different potential components, namely the ouabain-sensitive and the ouabain-insensitive components. The ouabain-sensitive component was enhanced by a moderate conditioning hyperpolarization. This component was most reasonably explained as a potential change generated by an activation of the electrogenic Na+ pump. The ouabain-insensitive potential component of the P-potential and the slow IPSP decreased in the amplitude and finally reversed its polarity by conditioning hyperpolarization. The reversal potential of ouabain-insensitive component of slow IPSP and slow inhibitory postsynaptic current (IPSC) was close to the EK [equilibrium potential for K+]. The amplitude of ouabain-insensitive component of P-potential and slow IPSP was markedly decreased by an elevation of external K+ concentration. The reversal potential of ouabain-insensitive component shifted to a more positive potential level in high K+ Ringer''s solution. It was augmented in K+-free Ringer''s solution. A reduction of the membrane resistance was observed during the generation of the slow IPSP, when the membrane potential of ganglion cells was held at a membrane potential level more negative than -60mV. The slow IPSC recorded by voltage-clamp method was associated with an increase in membrane conductance. The ouabain-insensitive component was generated by an activation of K+ conductance.