THE INFLUENCE OF MEMBRANE-POTENTIAL ON CHLORIDE CHANNELS ACTIVATED BYGABA IN RAT CULTURED HIPPOCAMPAL-NEURONS

Chloride currents were activated by a low concentration of GABA (0.5 m u M) in neonatal rat hippocampal neurons cultured for up to 14 days. C urrents elicited by 0.5 mu M GABA in neurons, voltage-clamped using th e whole-cell technique with pipettes containing 149 mM Cl-, reversed c lose to 0 mV whether pipettes contained 144 mM Na+ or 140 mM Cs+, and were blocked by 100 mu M bicuculline. Current-voltage curves showed ou tward rectification. Single channel currents appeared in cell-attached patches when the pipette tip was perfused with pipette solution conta ining 0.5 mu M GABA and disappeared when a solution containing 100 mu M bicuculline plus 0.5 mu M GABA was injected into the pipette tip. Th e channels showed outward rectification and, in some patches, had a mu ch lower probability of opening at hyperpolarized potentials. The aver age chord conductance in 10 patches hyperpolarized by 80 mV was 7.8 +/ - 1.6 pS (SEM) compared with a chord conductance of 34.1 +/- 3.5 pS (S EM) in the same patches depolarized by 80 mV. Similar single channel c urrents were also activated in cell-free, inside-out patches in symmet rical chloride solutions when 0.5 mu M GABA was injected into the pipe tte tip. The channels showed outward rectification similar to that see n in cell-attached patches, and some channels had a lower probability of opening at hyperpolarized potentials. The average chord conductance in 13 patches hyperpolarized by 80 mV was 11.8 +/- 2.3 pS (SEM) compa red with 42.1 +/- 3.1 pS (SEM) in the same patches depolarized by 80 m V.