GABAA receptor populations with novel subunit combinations and drug binding profiles identified in brain by alpha 5- and delta-subunit-specific immunopurification.
The pharmacological significance and structural basis of the gamma-aminobutyrate (GABAA) receptor heterogeneity was investigated in situ by an immunobiochemical analysis of receptor populations characterized by the delta- and alpha 5-subunit. Using an antiserum specific for the delta-subunit, a population of GABAA receptors (21 +/- 2% of solubilized receptors) was immunoprecipitated from rat brain extracts which contained high affinity benzodiazepine binding sites. They were distinguished from those immunoprecipitated by the alpha 1- and alpha 3-subunit antisera by a 4-5-fold and 5-10-fold higher affinity for diazepam and beta CCM, respectively. Using the delta-antiserum in immunoaffinity chromatography the delta-subunit was found to be associated with the alpha 1-, alpha 3-, beta 2/3-, and gamma 2-subunits, suggesting that the latter conveys benzodiazepine receptor sensitivity also to GABAA receptors containing the delta-subunit. The receptor population immunoprecipitated by the alpha 5-subunit antiserum (10 +/- 2% of receptors solubilized from whole brain extracts) was characterized by affinities for zolpidem, beta CCM, and CL 218872 which distinguished it from all other known receptor populations. The alpha 5-subunit was associated with the alpha 1-, alpha 3-, beta 2/3- and gamma 2-subunits pointing to differential subunit combinations. Indeed, when receptor populations were immunoprecipitated by the alpha 5-subunit antiserum from different brain regions, zolpidem displayed striking differences in affinity pointing to the role of subunits other than alpha 5 in determining receptor affinity.
Institute of Pharmacology, University of Zürich, Switzerland.
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S
Mertens
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Benke
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Mohler
D000818:Animals; D001569:Benzodiazepines / Q000378:metabolism; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism*; D002846:Chromatography, Affinity; D008297:Male; D010777:Photochemistry; D011233:Precipitin Tests; D051381:Rats; D011963:Receptors, GABA-A / Q000302:isolation & purification / Q000378:metabolism*
D011963:Receptors, GABA-A; D001569:Benzodiazepines