Allosteric interactions between gamma-aminobutyric acid, benzodiazepine and picrotoxinin binding sites in primary cultures of cerebellar granule cells. Differential effects induced by gamma- and delta-hexachlorocyclohexane.
Allosterism between gamma-aminobutyric acid (GABA), benzodiazepine and picrotoxinin recognition sites on the GABAA receptor was studied in primary cultures of cerebellar granule cells. The increase in [3H]flunitrazepam binding induced by GABA was inhibited by bicuculline and picrotoxinin and the decrease in [35S]t-butylbicyclophosphorothionate ([35S]TBPS) binding mediated by GABA was reverted by bicuculline. The effects of hexachlorocyclohexanes (the convulsant gamma- and the depressant delta-isomers, both acting at the picrotoxinin recognition site) on GABA and benzodiazepine sites were studied. delta-Hexachlorocyclohexane, but not the gamma-isomer (lindane), increased [3H]flunitrazepam binding in a concentration-dependent manner (EC50: 8.3 microM). This increase in [3H]flunitrazepam binding was reduced by bicuculline and picrotoxinin. The gamma-isomer reduced the increase in [3H]flunitrazepam binding induced by GABA or delta-hexachlorocyclohexane. Neither delta- nor gamma-hexachlorocyclohexane inhibited [3H]GABA binding. Moreover, the inhibition of [35S]TBPS binding induced by delta-hexachlorocyclohexane was not reverted by bicuculline. The results obtained in this study in vitro agree with the pharmacological properties and the effects of gamma- and delta-hexachlorocyclohexane in vivo. It is concluded that delta-hexachlorocyclohexane acts as a positive allosteric modulator and gamma-hexachlorocyclohexane acts as a non-competitive antagonist of the GABAA receptor.
Vale
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Department of Neurochemistry, Institut d'Investigacions Biomèdiques de Barcelona, CSIC, Barcelona, Spain.
Pomés
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Rodríguez-Farré
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Suñol
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D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005445:Flunitrazepam / Q000378:metabolism; D018756:GABA Antagonists / Q000494:pharmacology; D018757:GABA Modulators / Q000378:metabolism; D001556:Hexachlorocyclohexane / Q000737:chemistry / Q000494:pharmacology*; D007536:Isomerism; D007700:Kinetics; D051381:Rats; D011963:Receptors, GABA-A / Q000737:chemistry / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D018756:GABA Antagonists; D018757:GABA Modulators; D011963:Receptors, GABA-A; C037480:picrotoxinin receptor; D005680:gamma-Aminobutyric Acid; D001556:Hexachlorocyclohexane; D005445:Flunitrazepam; D001640:Bicuculline