Pentobarbital decreases the gamma-aminobutyric acidA receptor subunit gamma-2 long/short mRNA ratio by a mechanism distinct from receptor occupation.
Treatment with pentobarbital of primary cultured cerebellar granule cells decreased the gamma-aminobutyric acid, (GABA)A receptor subunit gamma-2 long/short (gamma-2L/S) mRNA ratio. A high dose of pentobarbital (500 microM) decreased the gamma-2L/S ratio by 64%; the decrease was dose and time dependent and reversible. (-)-Hexobarbital (500 microM), 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 microM 5alpha-pregnane-3alpha-ol-20-one) effect on the gamma-2L/S ratio. Furthermore, picrotoxin (10 microM), 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.
Tyndale
R F
RF
Addiction Research Foundation and Department of Pharmacology, University of Toronto, Canada. r.tyndale@utoronto.ca
Bhave
S V
SV
Hoffmann
E
E
Hoffmann
P L
PL
Tabakoff
B
B
Tobin
A J
AJ
Olsen
R W
RW
D000818:Animals; D000431:Ethanol / Q000494:pharmacology; D018757:GABA Modulators / Q000494:pharmacology*; D006591:Hexobarbital / Q000494:pharmacology; D010424:Pentobarbital / Q000494:pharmacology*; D010852:Picrotoxin / Q000494:pharmacology; D011280:Pregnanolone / Q000494:pharmacology; D012326:RNA Splicing; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000235:genetics
D000431:Ethanol; D018757:GABA Modulators; D006591:Hexobarbital; D010424:Pentobarbital; D010852:Picrotoxin; D011280:Pregnanolone; D012333:RNA, Messenger; D011963:Receptors, GABA-A