ROLE OF NITRIC-OXIDE PRODUCTION THROUGH M-2-CHOLINERGIC RECEPTORS IN CULTURED RAT VENTRICULAR MYOCYTES

We previously reported that carbachol (CCh) caused the enhancement of NO production coinciding with negative chronotropy in cultured rat ven tricular myocytes. In this study, we examined which subtype of muscari nic cholinergic receptor mediated these effects of CCh by measuring th e NOx production with an HPLC-Griess reaction system and monitoring th e beating with a Fotonic Sensor. The enhancement of NO production and negative chronotropy by 10(-4) M CCh stimulation were significantly in hibited by 10(-6) IM atropine, 10(-6) M methoctramine, 3 x 10(-4) M L- NMMA, and 10(-5) M methylene blue. On the other hand, 10(-6) M pirenze pine and 10(-6) M HHSiD had no influence on the negative chronotropy b y 10(-4) M CCh stimulation. Both 10(-6) M pirenzepine and 10(-6) M HHS iD suppressed the enhancement of NO production by 10(-4) M CCh stimula tion slightly though not statistically. In addition, the m2 cholinergi c receptor gene was expressed in our cell preparations, as demonstrate d by reverse-transcriptase/PCR analysis. We concluded that M-2-choline rgic receptor-mediated negative chronotropy may be due in part to acti vation of the NO-signaling pathway in cultured rat ventricular myocyte s. (C) 1998 Academic Press.