CARDIAC NITRIC OXIDE SYNTHASE ACTIVATION VIA C-TYPE NATRIURETIC PEPTIDE: ROLE OF MITOGEN-ACTIVATED PROTEIN KINASE PATHWAY IN HYPERTENSION: PP.22.390

Abstract

Objective: Antiproliferative actions of C-type natriuretic peptide (CNP) has been demonstrated in cardiac myocytes. In previous studies we demonstrated that CNP via NPR-C increases endothelial nitric oxide synthase (eNOS) activity in ventricle of spontaneously hypertensive rats (SHR). The aim was to examine eNOS expression and their phosphorylation levels in response to CNP in SHR heart and to investigate weather mitogen-activated protein kinase (MAPK) pathway is involved in this mechanism. Methods: A- In vivo studies: 12-weeks old SHR were intravenously infused with saline (NaCl 0.9%) or CNP (1 μg/Kg.min) during 60 minutes. Then animals were sacrificed by decapitation and NOS activity (using [14C] L-arginine as substrate), endothelial NOS (eNOS) expression and their phosphorylation levels (Western Blot) were determined in left ventricle. B- In vitro studies: NOS activity induced by CNP addition was determined in presence of: U-0126 (10 μM, p42/p44 MAPK inhibitor), LY 294002 (10 μM, PI3K inhibitor), SB 203580 (10 μM, p38 MAPK inhibitor), SP 600125 (10 μM, JNK 1/2 inhibitor) or PD 98059 (10 μM, MEK1/ERK 1 2 inhibitor), calmidazolium (10 μM, Cz, calmodulin antagonist) or pertussis toxin (800 ng/ml, PTx, Gi1–2 protein inhibitor). Results: A- In vivo: CNP increased NOS activity and eNOS phosphorylation levels but the peptide did not modify eNOS expression. B- In vitro: NOS stimulation induced by CNP was not modified by MAPK inhibitors but this activation was blocked by Gi protein or calmodulin inhibition. (NOS activity (pmol [14C] L-citrulline/mg.tissue.min): Basal activity = 351.9 ± 11.2; CNP = 417.1 ± 13.9*; U-0126 + CNP = 420.6 ± 8.7*; LY 294002 + CNP = 415.6 ± 13.5*; SB203580 + CNP = 422.8 ± 14.7*; SP600125 + CNP = 413.8 ± 9.8*; PD98059 + CNP = 418 ± 15.7*; Cz + CNP = 175.8 ± 21.3#; PTx + CNP = 356.5 ± 12.4#; *p < 0,01 vs basal activity; #p < 0,01 vs CNP induced activity, n = 6 each group). Conclusion: Cardiac antiproliferative actions attributed to CNP could be mediated by Ca2 + -calmodulin dependent eNOS activation. The mechanism would involve the interaction of CNP with NPR-C receptor and Gi1–2 protein activation without MAPK pathway participation in this model of hypertension.