1 Following identification of the human motilin receptor, we isolated the rabbit orthologue by PCR amplification and found this to be 85% identical to the open reading frame of the human receptor. The protein encoded was 84% identical to the human polypeptide. ]-motilin faded rapidly during its continual presence. Rat or human ghrelin 0.01 -10 mM were without activity. 4 Erythromycin 30 -3000 nM and 10 mM, respectively, increased neuronal activity and muscle tension in rabbit stomach. Unlike [Nle 13 ]-motilin, the increase in neuronal activity did not fade during continual presence of submaximally-effective concentrations of erythromycin; some fade was observed at higher concentrations. 5 We conclude that the pharmacology of the rabbit motilin receptor is similar to the human orthologue and, when expressed as a recombinant, comparable to the native receptor. However, in terms of their ability to increase neuronal activity in rabbit stomach, [Nle 13 ]-motilin and erythromycin are distinguished by different response kinetics, reflecting different rates of ligand degradation and/or interaction with the receptor.
The aim of this study was to characterize the pharmacological profile of the GABAB1/GABAB2 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.
The chimeric G‐protein, Gqi5, was used to couple receptor activation to increases in intracellular calcium for functional studies on the Fluorimetric Imaging Plate Reader (FLIPR), using a stable GABAB1/GABAB2/Gqi5 CHO cell line. [3H]‐CGP‐54626 was used in radioligand binding studies in membranes prepared from the same cell line.
The pharmacological profile of the recombinant GABAB1/B2 receptor was consistent with that of native GABAB receptors in that it was activated by GABA and baclofen and inhibited by CGP‐54626A and SCH 50911.
Unlike native receptors, the GABAB1/GABAB2/Gqi5 response was not inhibited by high microMolar concentration of phaclofen, saclofen or CGP 35348.
This raises the possibility that the GABAB1/GABAB2/Gqi5 recombinant receptor may represent the previously described GABAB receptor subtype which is relatively resistant to inhibition by phaclofen.
British Journal of Pharmacology (2000) 131, 1050–1054; doi:
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