Fluoride but not phorbol esters stimulate rat urinary bladder prostanoid synthesis: Investigations into the roles of G proteins and protein kinase C

The role of G proteins and protein kinase C in mediating muscarine receptor-linked prostanoid synthesis by the rat urinary bladder was investigated using the G protein activator, sodium fluoride (NaF); the protein kinase C activators, phorbol myristate (PMA) and phorbol dibutyrate (PDBU); the protein kinase C inhibitor, H7, and the parasympathomimetic, carbachol. NaF stimulated in vitro rat urinary bladder prostacyclin (PGI2) synthesis (EC50 = 6 mmol.l-1), an action inhibited by the presence of EDTA (10 mmol.l-1). Carbachol potentiated the stimulatory action of NaF. NaF (10 mmol.l-1)-stimulated PGI2 synthesis was inhibited by the calcium channel blockers verapamil, nifedipine and the protein kinase C inhibitor, H7, in concentration-dependent manners. Carbachol-stimulated PGI2 synthesis was also inhibited by H7. PDBU and PMA were without effect on de novo, NaF- or carbachol-stimulated urinary bladder PGI2 synthesis. Other prostanoids (PGF2 and PGF2 alpha) were stimulated to the ame degree as PGI2 by NaF, and inhibited equally by H7 and calcium channel blockers. Dibutyryl adenosine 3':5'-cyclic monophosphate was without effect on de novo or NaF-stimulated prostanoid synthesis. Since fluoride activates G proteins, these data indicate that: (1) muscarine receptor-prostanoid synthesis coupling is mediated by G proteins in the rat urinary bladder; (2) fluoride action is mediated by protein kinase C and not adenyl cyclase, probably through activation of phospholipase C and therefore the generation of the protein kinase C activator, diacyl glycerol; (3) activated protein kinase C may initiate Ca2++ mobilisation linked to prostanoid synthesis; and (4) the lack of effect of the phorbol esters on urinary bladder PGI2 synthesis, in contrast to that on other smooth muscle, indicates that in different smooth muscle tissues there are varying forms of protein kinase C.