Peroxynitrite Modulates The Expression of Gi Protein And Adenylyl Cyclase Signaling in Vascular Smooth Muscle Cells.

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We have further shown that vascular smooth muscle cells(VSMC) exposed to SNAP (NO donor)decreased the levels and functions of Giα proteins, which was restored to control levels by MnTBAP(peroxynitrite(ONOO-) scavenger) and not by ODQ(soluble guanylyl cyclase inhibitor) suggesting that NO-induced decreased Gi protein expression may be cGMP-independent and attributed to the increased levels of ONOO-. The present Studies were undertaken to investigate the role of ONOO- in the modulation of Gi protein expression in VSMC. A10 and aortic VSMC were used and treated with 3-Morpholinosydnonimine hydrochloride (SIN-1) or ONOO- for 24 hrs and the expression of Giα proteins was determined by immunoblotting techniques. SIN-1 and ONOO- decreased the expression of Giα-2 and Giα-3 proteins in a concentration manner. The maximal inhibition of about 30% and 40 % was observed at 0.5mM SIN-1 or at 0.5mM ONOO- in A-10 and VSM cells respectively. The decreased expression of Giα proteins was reflected in decreased Gi functions. Angiotensin II(AngII) and C-ANP4-23– mediated inhibitions of adenylyl cyclase were significantly attenuated by SIN-1 or ONOO- treatments. On the other hand, the expression of Gsα protein was not altered by these treatments in both types of cells, however, the stimulatory effects of isoproterenol, sodium fluoride (NaF) and forskolin (FSK) on adenylyl cyclase were significantly augmented. These results suggest that ONOO- decreased the expression of Gi proteins and associated functions in vascular smooth muscle cells. (supported by grant from Canadian Institutes of Health and Research)