The human GABA(B1b) and GABA(B2) heterodimeric recombinant receptor shows low sensitivity to phaclofen and saclofen.
1. The aim of this study was to characterize the pharmacological profile of the GABA(B1)/GABA(B2) heterodimeric receptor expressed in Chinese hamster ovary (CHO) cells. We have compared receptor binding affinity and functional activity for a series of agonists and antagonists. 2. The chimeric G-protein, G(qi5), was used to couple receptor activation to increases in intracellular calcium for functional studies on the Fluorimetric Imaging Plate Reader (FLIPR), using a stable GABA(B1)/GABA(B2)/G(qi5) CHO cell line. [(3)H]-CGP-54626 was used in radioligand binding studies in membranes prepared from the same cell line. 3. The pharmacological profile of the recombinant GABA(B1/B2) receptor was consistent with that of native GABA(B) receptors in that it was activated by GABA and baclofen and inhibited by CGP-54626A and SCH 50911. 4. Unlike native receptors, the GABA(B1)/GABA(B2)/G(qi5) response was not inhibited by high microMolar concentration of phaclofen, saclofen or CGP 35348. 5. This raises the possibility that the GABA(B1)/GABA(B2)/G(qi5) recombinant receptor may represent the previously described GABA(B) receptor subtype which is relatively resistant to inhibition by phaclofen.
Wood
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MD
Department of Neuroscience Research, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park, Third Avenue, Harlow, Essex, CM19 5AW. Martyn_Wood-1@sbphrd.com
Murkitt
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Rice
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Testa
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Punia
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Stammers
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Jenkins
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Elshourbagy
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Shabon
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Taylor
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Gager
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Minton
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Hirst
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Price
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Pangalos
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D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D018755:GABA Agonists / Q000378:metabolism*; D018756:GABA Antagonists / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D018079:Receptors, GABA / Q000378:metabolism*; D018080:Receptors, GABA-B / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D018755:GABA Agonists; D018756:GABA Antagonists; C485503:GABBR2 protein, human; D018079:Receptors, GABA; D018080:Receptors, GABA-B; C052329:phaclofen; D005680:gamma-Aminobutyric Acid; D001418:Baclofen; C080629:saclofen