EXTRACELLULAR ATP AND BRADYKININ INCREASE CGMP IN VASCULAR ENDOTHELIAL-CELLS VIA ACTIVATION OF PKC

Vasodilation by agents such as bradykinin and ATP is dependent on nitr ic oxide, the endothelium-dependent relaxing factor (EDRF). The releas e of EDRF results in elevation of cGMP in endothelial and smooth muscl e cells (9). The signaling pathway that leads to increases in cGMP is not completely understood. The role of protein kinase C (PKC) in the e levation of cGMP induced by ATP and bradykinin was studied in cultured porcine aortic endothelial cells, by measuring PKC phosphorylation of a substrate and by measuring cGMP levels by radioimmunoassay. Extrace llular ATP and bradykinin simultaneously elevated cGMP levels and PKC activity. The PKC inhibitors staurosporine, calphostin C, and Cremopho r EL (T. Tamaoki and H. Nakano. Bio/Technology 8: 732-735, 1990; F. K. Zhao, L. F. Chuang, NI. Israel, and R. Y. Chuang. Biochem. Biophys. R es. Commun. 159: 1359-1367, 1989) prevented the elevation of cGMP elic ited by ATP and reduced that produced by bradykinin. Cremophor did not affect the elevation of cGMP by nitroprusside, an agent that directly increases guanylate cyclase activity (9). The PKC activator phorbol 1 2-myristate 13-acetate, but not 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.