Loreclezole inhibition of recombinant alpha 1 beta 1 gamma 2L GABA(A) receptor single channel currents

Loreclezole had two different effects on GABA(A) receptor (GABAR) currents. When applied to GABARs that contained a beta 2 or beta 3 subunit subtype, but not a beta 1 subtype, loreclezole potentiated the peak current evoked b y sub-maximal concentrations of GABA. Loreclezole also increased the rate a nd degree of apparent desensitization of GABAR whole-cell currents, an effe ct that was independent of the beta subunit subtype, suggesting that potent iation and inhibition of GABAR current by loreclezole occurred through sepa rate sites. We used patch-clamp recording from outside-out and inside-out patches from L929 fibroblasts transiently transfected with rat GABAR subunits to examine the properties of inhibition of alpha 1 beta 1 gamma 2L single channel cur rents by loreclezole. Loreclezole decreased the mean open time of the chann el by decreasing the average durations of the open states. Loreclezole also increased the occurrence of a closed component with an average duration ne ar 20 ms. Inhibition by loreclezole was not voltage-dependent. Loreclezole was equally effective when applied to the intracellular side of the recepto r, suggesting that its binding site was readily accessible from both sides of the membrane. Pre-application of loreclezole effectively inhibited the G ABAR current in macropatches, indicating that binding did not require an op en channel. These findings were consistent with a mechanism of allosteric m odulation at a site formed by the membrane spanning regions of the receptor . (C) 2000 Elsevier Science Ltd. All rights reserved.