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Journal of Neuroscience, Vol 15, 6957-6962, Copyright © 1995 by Society for Neuroscience
GABA antagonists differentiate between recombinant GABAA/benzodiazepine receptor subtypes
H Luddens and ER Korpi
Laboratory of Molecular Neuroendocrinology, Center for Molecular Biology, Heidelberg, Germany.
Seventeen rat GABAA receptor subtypes were transiently expressed in the
human embryonic kidney 293 cell line from alpha 1, alpha 2, alpha 3, alpha
5, or alpha 6 variants with any of the three beta subunits and gamma 2S or
gamma 3. We obtained fingerprints in the form of subtype characteristic
concentration-response curves of 35S-TBPS binding to GABA and the GABAA
antagonists SR 95531 and bicuculline. alpha 3 beta 3 gamma 2S/3 and alpha 5
beta 3 gamma 2S/3 containing receptors effectively recognized 35S-TBPS but
not when beta 3 was replaced by the beta 1 or beta 2 subunit. This
indicates a specific interaction of alpha and beta variants to form
high-affinity 35S-TBPS binding sites. At low levels GABA allosterically
increased 35S-TBPS binding to all receptors with the concentration and
magnitude depending on the subunit combination. Exchange of the beta
variant did not alter the concentration-response curves for alpha 1 and
alpha 6 containing receptors but did so for alpha 2 containing receptors.
alpha 2 beta 3 gamma 3 receptors displayed strong GABA-induced stimulation
of 35S-TBPS binding, whereas binding to alpha 2 beta 3 gamma 3 receptors
was marginally increased. SR 95531 and bicuculline decreased 35S-TBPS
binding to all gamma 3 containing receptors. In addition, bicuculline was
effective on alpha 1 beta x gamma 2 receptors. SR 95531 was threefold more
potent than bicuculline in reversing GABA-induced modulation of 35S-TBPS
binding in most receptor types, but was 30-fold more potent on alpha 2 beta
1 gamma 3 and alpha 6 beta 1 gamma 2S receptors.(ABSTRACT TRUNCATED AT 250
WORDS)
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