GABA-evoked chloride currents do not differ between dendrites and somata of rat neocortical neurons

1. We performed patch-clamp recordings on acutely isolated somata and dendritic segments of rat neocortical neurons, in order to compare the reversal potential (E(GABA)) and relative density of GABA(A) receptor-mediated Cl(-) currents in these two cellular compartments. 2. Currents were recorded with the Cl(-)-impermeable pore former gramicidin (25--75 microg ml(-1)) in HCO(3)(-)-free bath solution. Voltage ramps (-110 to -30 mV) from a holding potential (V(h)) of -60 mV in the absence and presence of 2 microM GABA were used to construct instantaneous current-voltage relationships. Currents were abolished by co-application of GABA with the GABA(A) receptor antagonist bicuculline (40 microM). 3. GABA conductance, normalized to membrane surface area, was not different in somata and dendrites. In addition, E(GABA) was not different in the two compartments. 4. Replacement of intracellular K(+) with Cs(+) resulted in a significantly more depolarized E(GABA) in both somata and dendrites. These results suggest that the resting intracellular Cl(-) concentration ([Cl(-)](i)) is similar in somata and dendrites and that an outward Cl(-) transporter system maintains low [Cl(-)](i).