REGULATION OF ALLOSTERIC COUPLING AND FUNCTION OF STABLY EXPRESSED GAMMA-AMINOBUTYRIC-ACID (GABA)(A) RECEPTORS BY CHRONIC TREATMENT WITH GABA(A) AND BENZODIAZEPINE AGONISTS

Chronic treatments with drugs that stimulate or potentiate gamma-amino butyric acid (GABA)(A) receptor function cause uncoupling of allosteri c sites and downregulation of the GABA(A) receptors expressed in neuro ns. To study these effects on receptors having a defined subunit compo sition, we treated stably transfected mouse Ltk(-) cells (PA3 cells) w ith drugs known to uncouple GABA(A) receptors. Because dexamethasone c ontrols the expression of bovine alpha-1, beta-1 and gamma 2L GABA(A) receptor subunit genes in PA3 cells, this expression system provides a way to study receptors in the absence of neuronal subunit gene promot ers. We assayed binding of [H-3]flunitrazepam to measure allosteric co upling and uptake of Cl-36(-) to measure GABA(A) receptor function. Ch ronic (4 day) treatment of PA3 cells with muscimol, GABA or flunitraze pam reduced the GABA enhancement of binding of [H-3]flunitrazepam to P A3 cells. Chronic flurazepam or muscimol treatments also caused downre gulation of benzodiazepine potentiation of muscimol-stimulated Cl-36(- ) uptake. Chronic treatment with muscimol did not affect levels of sub unit mRNAS and alpha 1- or beta 1-subunit protein of GABA(A) receptors and chronic flunitrazepam did not affect subunit mRNAs or all protein . We conclude that chronic drug treatments regulate allosteric couplin g and function of GABA(A) receptors in stably transfected cells and th is regulation cannot be attributed to decreases in the expression of r eceptor subunits or to expression of subunits other than alpha 1, beta 1 or gamma 2L.