THE ANION SELECTIVITY OF GABA-MEDIATED POST-SYNAPTIC POTENTIALS IN MOUSE HIPPOCAMPAL CELLS

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Abstract
Intracellular recordings were made from CA1 and dentate cells of the mouse hippocampal slice. When potassium acetate was used to fill the electrodes, spontaneous synaptic activity was rarely seen in CA1 or dentate cells. In contrast, when electrodes filled with KCl were used, spontaneous depolarizing post-synaptic potentials (PSPS) were prominent. That these PSPS were mediated by GABA was supported by the following: they were blocked by electrophoretic application of bicuculline methiodide; their appearance was associated with the reversal of the evoked GABA-mediated recurrent inhibitory post-synaptic potential (IPSP) and their apeparance was associated with the positive displacement of the reversal potential for the response to GABA applied by electrophoresis close to the cell soma. The interval distribution for the PSPS could not be fitted by a Poisson distribution. The anionic selectivity of the conductance evoked by GABA was investigated by using the potassium salts of a range of anions to fill the electrodes. Depolarizing spontaneous PSPS were seen in all cells impaled with electrodes containing KCl, I, Br, nitrate, or chlorate. In these cells, the reversal potential for the response to electrophoretically applied GABA was displaced in the depolarizing direction and the evoked recurrent IPSP was reversed. When anions with hydrated shells larger than chlorate (bicarbonate, sulfate, chromate, acetate or citrate) were used, spontaneous depolarizing PSPS were not seen, and the reversal potential for the response to somatic GABA application and for the evoked recurrent IPSP lay between -70 and -75 mV.