IONIC MECHANISM ASSOCIATED WITH NONCHOLINERGIC SYNAPTIC INHIBITION IN MOLLUSCAN NEURONS

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Abstract
The problem was analyzed in snail Cryptomphallus aspersa by intracellular recording. Increase of intra-cellular concentration of Cl- or by replacement of external Cl by SO4 [long dash]did not affect the non-cholinergic postsynaptic potentials and/or its reversal potential. In K-free medium the amplitude of the inhibitory potentials is nearly doubled. Stepwise increases of outer potassium from 4.9 mM to 40 mM provokes a gradual diminution of the amplitude of inhibitory potentials. Plotting the inversion potential values against the log of outer K+ concentration, a straight line may be drawn presenting a slope of -35 mV for a tenfold (K)0 change, less steep than that predicted by the Nernst equation. Factors explaining this difference are discussed. Then non-cholinergic inhibitory potentials possibly result from an increase of the permeability of subsynaptic membrane that allows a selective movement of K+ down its electrochemical gradient.