PENTOBARBITAL DECREASES THE GAMMA-AMINOBUTYRIC ACID(A) RECEPTOR SUBUNIT GAMMA-2 LONG SHORT MESSENGER-RNA RATIO BY A MECHANISM DISTINCT FROMRECEPTOR OCCUPATION/

Treatment with pentobarbital of primary cultured cerebellar granule ce lls decreased the gamma-aminobutyric acid, (GABA)(A) receptor subunit gamma-2 long/short (gamma-2L/S) mRNA ratio. A high dose of pentobarbit al (500 mu M) decreased the gamma-2L/S ratio by 64%; the decrease was dose and time dependent and reversible. (-)-Hexobarbital (500 mu M), t he 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 l ittle (2 mu M 5 alpha-pregnane-3 alpha-ol-20-one) effect on the gamma- 2L/S ratio. Furthermore, picrotoxin (10 mu M), which blocks the GABA- and pentobarbital-activated GABA(A) receptor channel, neither changed the gamma-2L/S ratio nor blocked the pentobarbital-induced changes. Th ese data suggest that barbiturates alter the gamma-2L/S mRNA ratio by a mechanism that does not require GABA(A) receptor activation. The gam ma-2L/S subunit mRNA includes an exon encoding an octapeptide that con tains a protein kinase C phosphorylation consensus site. This exon-enc oded peptide, occurring in the putative intracellular loop, can be pho sphorylated, and in vitro, this phosphorylation has been shown to have functional consequences. This is the first report of a drug-induced a lteration in receptor mRNA splicing. Furthermore, the changes in the g amma-2L/S ratio produced by pentobarbital exposure may have significan t effects on the function of an important brain protein, the GABA(A) r eceptor.