Analysis of slow inhibitory postsynaptic potential of bullfrog sympathetic ganglion.

Abstract

F he P potential (slow IPSP or inhibitory postsynaptic potential) of nico-tinized bullfrog sympathetic ganglia was studied by means of the sur-rose-gap method. The P potential was diminished and eventually abolished by conditioning depolarization of ganglion cells, whereas it was enhanced by moderate conditioning hyperpolarization, and was diminished and eventually abolished by intense conditioning hyperpolarization. In both Ringer and K-rich Ringer solutions, the abolition of the P potential by conditioning hyperpolarization occurred at a level beyond the K-equilibrium potential, as indicated by the reversal level of the after-hyperpolarization of the ganglionic action potential. In low -K Ringer solution the P potential was diminished while the reversal level of the after -hyperpolarization was shifted toward greater negativity. No change in the P potential was observed when the external Cl ions were totally replaced with glutamate ions. The P potential is apparently independent of the K- and Cl-equilibrium potentials of the cell membrane. The experimental fact that the P potential was markedly enhanced and prolonged after the ganglion was perfused with a Na-rich Ringer solution suggested that the P potential may be produced by synaptic activation of an electrogenic Na pump in the ganglion cells.