Sodium dependency of GABA uptake into glial cells in bullfrog sympathetic ganglia

Abstract

The kinetics of sodium dependency of GABA uptake by satellite glial cells was studied in bullfrog sympathetic ganglia. GABA uptake followed simple Michaelis-Menten kinetics at all sodium concentrations tested. Increasing external sodium concentration increased both Km and Vmax for GABA uptake, with an increase in the Vmax/Km ratio. The initial rate of uptake as a function of the sodium concentration exhibited sigmoid shape at 100 microM GABA. Hill number was estimated to be 2.0. Removal of external potassium ion or 10 microM ouabain reduced GABA uptake time-dependently. The effect of ouabain was potentiated by 100 microM veratrine. These results suggest that at least two sodium ions are involved with the transport of one GABA molecule and that sodium concentration gradient across the plasma membrane is the main driving force for the transport of GABA. The essential sodium gradient may be maintained by Na+, K(+)-ATPase acting as an ion pump.