Blunted furosemide action on cerebellar GABAA receptors in ANT rats selectively bred for high alcohol sensitivity.
Furosemide specifically reverses the inhibition by gamma-aminobutyric acid (GABA) of t-[35S]-butylbicyclophosphorothionate ([35S]TBPS) binding and increases the basal [35S]TBPS binding to the cerebellar granule cell layer GABAA receptors. For the selectivity of furosemide, an interplay between GABAA receptor alpha 6 and beta 2 or beta 3 subunits is needed. We have now investigated the furosemide sensitivity of cerebellar [35S]TBPS binding in the alcohol-sensitive (ANT) rat line that harbors a pharmacologically critical point mutation in the alpha 6 subunit [alpha 6 (Q1000)], increasing benzodiazepine affinity of the normally insensitive alpha 6-containing receptors. ANT receptors were less efficiently affected by furosemide, while a normal GABAA receptor antagonism was observed with a specific GABAA receptor antagonist SR 95531. Reduced [3H]muscimol binding in ANT samples and small alterations in situ hybridization signals for alpha 1, alpha 6, beta 2, beta 3, gamma 2 and delta subunit mRNAs failed to correlate with impaired cerebellar furosemide efficacy in individual animals. The alpha 6 (q100) ANT mutation was not responsible for the reduced efficacy of furosemide in the ANT rat line, as judged from the potent furosemide antagonism in recombinant ANT-type alpha 6 (Q100)beta 3 gamma 2 receptors. This data suggest that presence of a novel abnormality in the structure and/or expression of alpha 6 subunit-containing GABAA receptors in the ANT rat line.
Mäkelä
R
R
Department of Alcohol Research, National Public Health Institute, Helsinki, Finland.
Lehtonen
M
M
Wisden
W
W
Lüddens
H
H
Korpi
E R
ER
D000818:Animals; D001345:Autoradiography; D002460:Cell Line; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D002531:Cerebellum / Q000187:drug effects*; D004232:Diuretics / Q000494:pharmacology*; D000431:Ethanol / Q000494:pharmacology*; D005260:Female; D005665:Furosemide / Q000494:pharmacology*; D018755:GABA Agonists / Q000378:metabolism; D058787:GABA-A Receptor Antagonists; D006801:Humans; D017403:In Situ Hybridization; D008024:Ligands; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011963:Receptors, GABA-A / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D002492:Central Nervous System Depressants; D004232:Diuretics; D018755:GABA Agonists; D058787:GABA-A Receptor Antagonists; D008024:Ligands; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D000431:Ethanol; D005665:Furosemide