Angiotensin II Modulates ANP-R2/ANP-C Receptor-mediated Inhibition of Adenylyl Cyclase in Vascular Smooth Muscle Cells: Role of Protein Kinase C

In the present studies, we have investigated the modulation of atrial natriuretic peptide (ANP) receptor of R2 subtype (ANP-R2/ANP-C) coupled to adenylyl cyclase/cAMP signal transduction system by angiotensin II (angII). C-ANF4–23[des(Gln18, Ser19, Gln20, Leu21, Gly22)ANF4–23-NH2] and AngII inhibited adenylyl cyclase activity in a concentration-dependent manner in vascular smooth muscle cells (VSmc A-10). The maximal inhibitions observed were about 40 and 30%, respectively, with an apparent Kiof about 1 and 10 n . Pretreatment of the cells with AngII resulted in the attenuation of both C-ANF4–23and AngII-mediated inhibitions of adenylyl cyclase, without altering [125I]-ANF binding. The levels of Giα-2and Giα-3proteins as determined by immunoblotting were also augmented by AngII treatment. In addition, AngII treatment stimulated the phosphorylation of Giα2but not of Giα3or ANP-C receptor, as revealed by immunoprecipitation of the proteins using specific antibodies after prelabelling the cells with [32P]orthophosphate. Staurosporine and chelerythrine, protein kinase C (PKC) inhibitors at 1 and 100 n , respectively, prevented the AngII-mediated desensitization of C-ANF4–23-sensitive adenylyl cyclase. In addition, the AngII-mediated phosphorylation of Giα2protein was also inhibited partially by about 35% by staurosporine treatment. These results suggest that the attenuation of C-ANF4–23-mediated inhibition of adenylyl cyclase activity by AngII may not be attributed to the downregulation of receptors or to the decreased levels of G-proteins, and may involve PKC-dependent mechanisms.