Physiological properties of GABA(A) receptors from acutely dissociated ratdentate granule cells

Study of fast, GABA, receptor-mediated, inhibitory postsynaptic currents (T PSCs) in hippocampal dentate granule cells has suggested that properties of GABA(A) receptors influence the amplitude and time course of the IPSCs. Th is study describes the physiological properties of GABA(A) receptors presen t on hippocampal dentate granule cells-acutely isolated from 18- to 35-day- old rats. Rapid application of 1 mM GABA to outside-out macropatches excise d from granule cells produced GABA(A) receptor currents with rapid rise tim e and biexponential decay of current after removal of GABA. After activatio n,: granule cell GABA(A) receptor currents desensitized incompletely. Durin g a 400-ms application of 1 mM GABA(A) peak current only desensitized simil ar to 40%. In symmetrical chloride solutions there was no outward rectifica tion of whole cell current. Activation rates and peak currents elicited by rapid application of GABA to macropatches were also similar at positive and negative holding potentials. However, deactivation of GABA(A) receptor cur rents was slower at positive holding potentials. When whole cell currents w ere recorded without ATP in the pipette, current run-down was not apparent for 30 min in 50% of neurons, but run-down appeared to start soon after acc ess was established in the remaining neurons. When 2 mM ATP was included in the recording pipette no run-down was apparent in 30 min of recording. The efficacy and potency of GABA were lower in cells recorded with no ATP in t he pipette and during run-down compared with those recorded with 2 mM ATP a nd no run-down.