High glucose augmented Gaq‐mediated cell signaling in vascular smooth muscle cells (VSMC): role of oxidative stress

Abstract

We have previously shown that Gai protein expression and associated adenylyl cyclase signaling was decreased in VSMC in hyperglycaemia and diabetes. In the present studies we have examined the effect of hyperglycaemia on the expression of Gaq and phospholipase C b-1 (PLCb-1) proteins and associated inositol-triphosphate (IP3) turnover signaling in A10 VSMC. A10 cells were incubated with 5.5 mM (control) and 26 mM (Hyperglycaemia) glucose for different time periods (1 to 5 days) at 37 0C. The levels of Gaq and PLCb-1 proteins as determined by immunoblotting were significantly augmented in hyperglycaemic (HG) cells as compared to control cells after 3 days of treatment. Endothelin-1 (ET-1) augmented the IP3 formation in both control and HG cells, however, the increase was significantly higher in HG cells as compared to control cells. On the other hand, the basal levels of IP3 were not significantly different between the two groups. The superoxide anion (O2-) formation measured by the lucigenin-enhanced chemiluminescence method and the levels of NADPH oxidase sununits p47 and p22 were significantly enhanced in HG cells. Futhermore, the antioxidant diphenyleneiodonium (DPI) attenuated the ET-1- induced increased formation of IP3 and enhanced expression of PLCb-1 towards control levels. These results suggest that enhanced oxidative stress induced by hyperglycaemia may be responsible for the augmented expression of Gaq and PLCb-1 proteins and thereby enhanced ET-1-induced IP3 turnover in VSMC. (Supported by a grant from the QHF).