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 dendr itic segments of rat neocortical neurons, in order to compare the reversal potential (E-GABA) and relative density of GABA(A) receptor-mediated Cl- cu rrents in these two cellular compartments. 2. Currents were recorded with the Cl--impermeable pore former gramicidin ( 25-75 mug ml(-1)) in HCO3--free bath solution. Voltage ramps (-110 to -30 m V) from a holding potential (V-h) of -60 mV in the absence and presence of 2 muM GABA were used to construct instantaneous current-voltage relationshi ps. Currents were abolished by co-application of GABA with the GABA(A) rece ptor antagonist bicuculline (40 muM). 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 mor e depolarized E-GABA in both somata and dendrites. These results suggest th at the resting intracellular Cl- concentration ([Cl-](i)) is similar in som ata and dendrites and that an outward Cl- transporter system maintains low [Cl-](i).