Role of nitric oxide production in carbachol-induced negative chronotropy in cultured rat ventricular myocytes.

It has been reported that nitric oxide (NO) plays a physiological role in mediating the effect of vagal stimulation in the autonomic regulation of the heart. In this study, the changes in NO production induced by carbachol were investigated by measuring the NO metabolites, nitrite (NO2-) and nitrate (NO3-), with a high-performance liquid chromatography-Griess reaction system, and the carbachol-induced chronotropic response was simultaneously investigated. Cultured rat ventricular myocytes exhibited a dose-dependent negative chronotropic response and NO metabolite production in response to carbachol. The negative chronotropy and the enhancement of NO metabolite production induced by 10(-4) M carbachol were completely abolished by 10(-6) M atropine. Both of these effects of carbachol were completely abolished by NO synthase inhibitors such as 3 X 10(-4) M NG-monomethyl-L-arginine acetate and 10(-5) M methylene blue. Furthermore, the negative chronotropic effect induced by 10(-4) M carbachol was also abolished by 10(-6) M 1 H-[1,2,4]oxadiazolo[4,3-alpha]quanoxalin-1-one, a selective guanylyl cyclase inhibitor. In addition, 10(-4) M 8-bromoguanosine 3':5'-cyclic monophosphate, a cell-permeable analogue of guanosine 3':5'-cyclic monophosphate, caused a negative chronotropic effect. These results suggest that the NO-signaling pathway may play an important role in the muscarinic cholinergic regulation of myocardial function.