Extracellular ATP and bradykinin increase cGMP in vascular endothelial cells via activation of PKC

Vasodilation by agents such as bradykinin and ATP is dependenton nitric oxide, the endothelium-dependent relaxing factor (EDRF). Therelease of EDRF results in elevation of cGMP in endothelial and smoothmuscle cells (9). The signaling pathway that leads to increases in cGMPis not completely understood. The role of protein kinase C (PKC) in theelevation of cGMP induced by ATP and bradykinin was studied in culturedporcine aortic endothelial cells, by measuring PKC phosphorylation of asubstrate and by measuring cGMP levels by radioimmunoassay.Extracellular ATP and bradykinin simultaneously elevated cGMP levelsand PKC activity. The PKC inhibitors staurosporine, calphostin C, andCremophor EL (T. Tamaoki and H. Nakano.Bio/Technology 8: 732-735, 1990; F. K. Zhao, L. F. Chuang, M. Israel, and R. Y. Chuang. Biochem. Biophys.Res. Commun. 159: 1359-1367, 1989) prevented theelevation of cGMP elicited by ATP and reduced that produced bybradykinin. Cremophor did not affect the elevation of cGMP bynitroprusside, an agent that directly increases guanylate cyclaseactivity (9). The PKC activator phorbol 12-myristate 13-acetate, butnot a phorbol ester analog inactive on PKC, also elevated cGMP levels.These results suggest that EDRF agonists elevate cGMP in endothelial cells via PKC stimulation.