High-affinity copper block of GABAA receptor-mediated currents in acutely isolated cerebellar Purkinje cells of the rat

The actions of Cu2+ ions on GABA(A) receptor-mediated currents in acutely isolated Purkinje cells from rat cerebellum were studied using the whole-cell patch-clamp technique and a rapid perfusion system. Bath application of Cu2+ reduced currents induced by 2 mu M gamma-aminobutyric acid (GABA) in a concentration-dependent manner with an IC50 of 35 nM. The Cu2+-induced block of GABA responses was not voltage-dependent. Increasing the GABA concentration (from 2 to 50 mu M) decreased the blocking effect of Cu2+, Dose-response analysis for activation of GABA(A) receptors revealed a twofold decrease in apparent affinity for GABA in the presence of 0.1 mu M Cu2+. Recovery from the block required several minutes after removal of Cu2+ from the medium. The block was removed by histidine, which preferentially forms complexes with Cu2+, or by other chelating substances. Application of 10 mu M histidine immediately before application of 2 mu M GABA completely relieved the block of GABA responses produced by 0.1 mu M Cu2+. Th, effect of histidine was concentration-dependent with an EC50 Of 0.75 mu M. The results demonstrate that Cu2+ is a potent inhibitor of GABA-evoked responses in rat Purkinje cells. Copper may be an endogenous synaptic modulating factor. Cu2+ toxicity, notably in Wilson's disease, could result to some extent from chronic GABA(A) receptor blockade.