Excitatory effect of amino acids on identified neuron R14 of Aplysia. I. Glycine-induced depolarization and its ionic mechanism.

The ionic mechanism of the membrane effect of glycine on identified neuron R14 of Aplysia was investigated with conventional intracellular recording and voltage-clamp techniques. Both localized and bath applications of glycine markedly depolarize R14. Bath-applied glycine induced an inward current that gradually reached a maximum and remained at that level until glycine was washed out. Displacement of the holding potential from -46 to -121 mV increased the inward current. The extrapolated reversal potential was +38.6 mV. Reduction of [Na+]o reversibly decreased the inward current. Alterations of [K+]O, [Cl-]O, and [Ca2+]O, as well as bath-applied ouabain and sodium cyanide, did not affect the inward current. These results suggest that glycine can induce an Na+ current and that the glycine-induced inward current does not reflect an active uptake by an Na+-coupled transport system of glycine into the neuron.