Molecular modulation of recombinant rat alpha1beta2gamma2 GABA(A) receptor channels by diazepam

Recombinant gamma-aminobutyric acid (GABA(A)) receptor channels containing alpha1beta2gamma2-subunits were transiently expressed in HEK293 cells. Modulation by diazepam (DZ) was investigated using the patch-clamp technique with a device for ultra-fast solution exchange. GABA activated Cl(-)-currents were potentiated when DZ > 0.1 microM was added to non-saturating concentrations of GABA (< 0.1 mM GABA). Maximal potentiation of the peak current amplitude by a factor of 2.5 was observed when 1 microM DZ was added to the test-solution. Deactivation of GABA-activated currents after the end of GABA pulses was best fitted with two time constants. After application of DZ + GABA, increase of time constants of deactivation was measured. It was independent on GABA concentration. We conclude that prolongation of deactivation after application of GABA + DZ may be an important mechanism of the modulatory action of DZ at GABA(A) receptor channels.