Serotonin (5-HT) potently contracts the fundus of the rat stomach; however, the associated transduction pathway has not been described fully. Experiments were performed in an attempt to gain insight into the coupling mechanism associated with this fundal 5-HT receptor. 5-HT-stimulated [35S]GTPγS binding to a protein which was recognized by anti-Gαz antiserum in a Mg++-dependent fashion. 5-HT increased [35S]GTPγS binding in the fundus, but not in the corpus of the rat stomach. 5-HT also enhanced the binding of [α-32P]GTP to the fundal protein and increased the hydrolysis of GTP to GDP in fundal membranes. The fundal protein which binds GTP is 25 to 29 kDa in size whereas the brain Gαz protein which is recognized by the anti-Gαz antibody is a 41 kDa protein. Mixing experiments revealed that the fundal guanine nucleotide binding protein does not appear to be a proteolytic product of the 41 kDa Gαz protein. Activating protein kinase C with phorbol-12-myristate, 13-acetate induced a concentration- dependent, noncompetitive inhibition of [35S]GTPγS binding to the fundal protein, and of 5-HT-induced contraction of fundal strips. Porbol-12- myristate, 13-acetate did not alter carbachol- or KCl-mediated fundus contraction. Furthermore, the activation of [35S]GTPγS binding by serotonergic agonists and its inhibition by pharmacological antagonists corresponded to the known actions of these agents on contraction of fundal muscle. The results provide evidence that the 5-HT receptor in the rat stomach fundus is coupled directly or indirectly to a Gαz-like protein which may mediate 5-HT-induced contraction in this tissue.
|Number of pages||10|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - 1993|