The human 5-ht5A receptor couples to Gi/Go proteins and inhibits adenylate cyclase in HEK 293 cells

The G protein coupling of human 5-hydroxytryptamine(5A) (h5-ht(5A)) receptors was investigated in stably transfected human embryonic kidney (HEK) 293 cells, using radioligand and guanosine-5'[gamma-S-35]thiotriphosphate binding to membranes and cyclic adenosine monophosphate measurements in cells. 5-Carboxamido[H-3]tryptamine bound to high- and low-affinity sites on h5-h(5A)-HEK 293 cell membranes. Guanylyl-imidodiphosphate addition and pertussis toxin pre-treatment abolished high-affinity binding, indicating coupling to G proteins of the G(i)/G(o) family. [N-methyl-H-3]Lysergic acid diethylamide bound to a single site; guanylyl-imidodiphosphate and pertussis toxin did not alter lysergic acid diethylamide affinity. 5-Hydroxytryptamine stimulated guanosine-5'[gamma-S-35]thiotriphosphate binding to 130% over basal and this effect was completely abolished by pertussis toxin. Various 5-hydroxytryptamine receptor ligands were tested for inhibition of 5-carbaxamido[H-3]tryptamine binding and in guanosine-5'[gamma-S-35]thiotriphosphate binding assays. 5-Hydroxytryptamine consistently inhibited forskolin-induced cyclic adenosine monophosphate formation by 25% in h5-ht(5A)-HEK 293 cells; no effect was detected on basal cyclic adenosine monophosphate levels, on intracellular Ca2+ concentration or arachidonic acid release. Our studies demonstrate functional coupling of the h5-ht(5A) receptor to pertussis toxin-sensitive G proteins and to inhibition of adenylate cyclase activity. (C) 1998 Elsevier Science B.V. All rights reserved.