Characteristics of GABAA channels in rat dentate gyrus

Single channel currents were activated by GABA (0.5 to 5 m) in cell-attached and inside-out patches from cells in the dentate gyrus of rat hippocampal slices. The currents reversed at the chloride equilibrium potential and were blocked by bicuculline (100 m). Several different kinds of channel were seen: high conductance and low conductance, rectifying and nonrectifying. Channels had multiple conductance states. The open probability (P _o ) of channels was greater at depolarized than at hyperpolarized potentials and the relationship between P _o and potential could be fitted with a Boltzmann equation with equivalent valency (z) of 1. The combination of outward rectification and potentialdependent open probability gave very little chloride current at hyperpolarized potentials but steeply increasing current with depolarization, useful properties for a tonic inhibitory mechanism.