5-HYDROXYTRYPTAMINE-STIMULATED ACCUMULATION OF 1,2-DIACYLGLYCEROL IN THE RABBIT BASILAR ARTERY - A ROLE FOR PROTEIN-KINASE-C IN SMOOTH-MUSCLE CONTRACTION

1 5-Hydroxytryptamine (5-HT) produced a concentration-dependent increase in the membrane concentration of 1,2-diacylglycerol (DG) in the rabbit isolated basilar artery, but did not stimulate the hydrolysis of membrane phosphoinositide. 2 The 5-HT-induced accumulation of DG could be blocked with the putative phospholipase C inhibitor 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC; 70-mu-M), but not with the protein kinase C inhibitor, 1-(5-isoquinolinesulphonyl)-2-methyl piperazine (H7; 50-mu-M). 3 Direct stimulation of protein kinase C with phorbol 12,13-dibutyrate (PDBu) produced sustained smooth muscle contraction which was fairly rapid in onset and could be reversed by H7 but not by NCDC. The inactive phorbol, 4-alpha phorbol 12,13-didecenoate, did not produce contraction in the basilar artery. 4 5-HT-induced contractions (1 nM-100-mu-M) were blocked or greatly reduced in the presence of the protein kinase inhibitor H7 or polymyxin B, and with the phospholipase C inhibitor, NCDC. The concentrations of these inhibitors which abolished contraction to 5-HT, did not alter smooth muscle contraction produced in response to 30 mM K+ -physiological salt solution (PSS). 5 These data suggest that DG production and the subsequent activation of PKC forms an important component of the cerebrovascular contractile response to 5-HT. As the DG does not appear to arise from membrane phosphatidylinositol, it appears that 5-HT can stimulate the production of this second messenger in cerebral arteries by a mechanism which is different from peripheral arteries.