IONIC MECHANISMS OF THE SLOW INHIBITORY POSTSYNAPTIC POTENTIAL OF SYMPATHETIC GANGLION CELLS IN BULLFROGS

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The nature of P-potential of bullfrog sympathetic ganglia of which nicotinic transmissions were completely blocked by d-TC (1.4 mM) was analysed by the sucrose-gap method. The P-potential reversed its polarity during conditioning hyperpolarizations at a potential level which appeared to be the K⁺ -equilibrium potential, and only a small fraction of the Ppotential was depressed by ouabain (2×10^-3 mM). These natures of the Ppotential were different from those of the P-potential of nicotinized ganglia which were analysed in our previous experiments. The ionic mechanism underlying the P-potential was discussed on the basis of the present results together with our previous results obtained from nicotinized ganglia, and it was suggested that the P-potential (slow IPSP) was composed with, at least, two different components, viz. an activation of the electrogenic Na⁺ pump and increase of K⁺ conductance of the subsynaptic membrane.