Vol. 283, Issue 1, 350-357, 1997

Pentobarbital Decreases the -Aminobutyric Acid_A Receptor Subunit gamma-2 Long/Short mRNA Ratio by a Mechanism Distinct from Receptor Occupation¹

R. F. Tyndale, S. V. Bhave, E. Hoffmann, P. L. Hoffman, B. Tabakoff, A. J. Tobin and R. W. Olsen

Addiction Research Foundation and Department of Pharmacology, University of Toronto, Toronto, M5S 1A8, Canada (R.F.T., E.H.); Department of Pharmacology, University of Colorado Health Sciences Center, Denver, Colorado (S.V.B., P.L.H., B.T.); and Departments of Neurology, Physiological Sciences (A.J.T.) and Molecular and Medical Pharmacology (R.W.O.), and the Brain Research Institute University of California, Los Angeles (A.J.T., R.W.O.).

Treatment with pentobarbital of primary cultured cerebellar granule cells decreased the -aminobutyric acid, (GABA)_A receptor subunit gamma-2 long/short (gamma-2L/S) mRNA ratio. A high dose of pentobarbital (500 µM) decreased the gamma-2L/S ratio by 64%; the decrease was dose and time dependent and reversible. ()-Hexobarbital (500 µM), the less potent stereoisomer for GABA_A receptor activation, decreased the ratio slightly (30%) but significantly more than (+)-hexobarbital (20%). Other GABA_A receptor activators had no (100 mM ethanol) or little (2 µM 5-pregnane-3-ol-20-one) effect on the gamma-2L/S ratio. Furthermore, picrotoxin (10 µM), which blocks the GABA- and pentobarbital-activated GABA_A receptor channel, neither changed the gamma-2L/S ratio nor blocked the pentobarbital-induced changes. These data suggest that barbiturates alter the gamma-2L/S mRNA ratio by a mechanism that does not require GABA_A receptor activation. The gamma-2L/S subunit mRNA includes an exon encoding an octapeptide that contains a protein kinase C phosphorylation consensus site. This exon-encoded peptide, occurring in the putative intracellular loop, can be phosphorylated, and in vitro, this phosphorylation has been shown to have functional consequences. This is the first report of a drug-induced alteration in receptor mRNA splicing. Furthermore, the changes in the gamma-2L/S ratio produced by pentobarbital exposure may have significant effects on the function of an important brain protein, the GABA_A receptor.