γ-Aminobutyric acid(A) receptor function is desensitised in rat cultured cerebellar granule cells following chronic flunitrazepam treatment

Abstract

This study examined γ-aminobutyric acid(A) (GABA(A)) receptor function in cultured rat cerebellar granule cells by using microphysiometry following chronic flunitrazepam exposure, and correlated the findings with the α1 and β2/3 subunit protein expression and [3H]-muscimol binding after the same treatment paradigm. Flunitrazepam treatment reduced (p < 0.05) the maximal GABA-stimulated increase in extracellular acidification rate (E(max)) (16.5 ± 1.2% and 11.3 ± 1.0%, 2-day control and treated cells, respectively; 17.4 ± 1.0% and 9.9 ± 0.7%, 7-day control and treated cells, respectively; best- fit E(max) ± SEM, n = 7), without affecting the GABA concentration required to elicit 50% of maximal response (EC50) (1.2 ± 1.7 and 2.3 ± 1.8 μM, 2- day control and treated cells, respectively; 1.7 ± 1.5 and 1.5 ± 1.5 μM, 7-day control and treated cells, respectively; best-fit EC50 ± SEM, n = 7). Flunitrazepam exposure also abolished the flunitrazepam potentiation of the GABA response, caused a transient reduction of the GABA(A) receptor α1 and β2/3 subunit proteins over the initial 2 days, but did not alter [3H]muscimol binding compared with vehicle-treated cells. The results suggest that changes in GABA(A) receptor subunit protein expression, rather than loss of [3H] muscimol binding sites, underlie the chronic flunitrazepam-mediated desensitisation of GABA(A) receptor function.