Pertussis toxin treatment prevents 5-HT(5a) receptor-mediated inhibition of cyclic AMP accumulation in rat C6 glioma cells |
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Authors: | Thomas E A Matli J R Hu J L Carson M J Sutcliffe J G |
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Affiliation: | Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA. |
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Abstract: | We have investigated the functional coupling of the rat 5HT(5a) receptor subtype to adenylate cyclase in a rat C6 glioma cell line. In 5HT(5a) receptor-transfected cells, 5HT caused a concentration-dependent inhibition of forskolin-stimulated cAMP accumulation, with an EC(50) value of 41 nM and a maximal effect of 57% inhibition. This effect was dependent on the concentration of forskolin used to elevate cAMP levels. Methiothepin (1 mcM), which has high affinity for the 5HT(5a) receptor, antagonized the 5HT(5a) receptor-mediated inhibition, and unmasked a stimulation of cAMP formation similar to that observed in untransfected cells, whereas ketanserin (0.1 mcM) enhanced the inhibitory effect of 5HT. Pertussis toxin treatment (0.5 mcg/ml) completely blocked the inhibitory effect of 5HT on cAMP formation, also revealing increase in cAMP accumulation. Pretreatment of the transfected membranes with pertussis toxin abolished subsequent ADP-ribosylation of a 41 kDa protein, correlating the cAMP effect with a functional uncoupling of an inhibitory G protein from its receptor. These results demonstrate an efficient functional coupling of the rat 5HT(5a) receptor to the inhibition of adenylate cyclase via a pertussis toxin-sensitive G[alpha(i)], inhibitory G-protein. |
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