Peroxynitrite modulates receptor-activated Ca2+ signaling in vascular endothelial cells

Peroxynitrite (ONOO-) is formed from superoxide (O-2(-)) and . NO. We have previously reported that O-2(-) does not alter endothelial cell Ca2+ signaling. To test whether . NO alters Ca2+ signaling, cells were incubated with the . NO donor, spermine NONOate. Neither spermine NONOate nor S-nitroso-N-acetyl penicillamine (SNAP) altered bradykinin-stimulated Ca2+ signaling. By contrast, 3-morpholinosydnonimine (SIN-1), which generates ONOO- by releasing O-2(-) and . NO essentially in a simultaneous manner, significantly inhibited signaling. Initially, the inhibitory effect of 1 mM SIN-1 was selective toward agonist-stimulated influx of external Ca2+. At later time points, SIN-1 additionally depleted internal stores of releasable Ca2+. When cells were coincubated with SIN-1 plus superoxide dismutase, a technique designed to scavenge O-2(-) and convert SIN-1 to purely an . NO-donor compound, Ca2+ signaling was identical to control. SIN-1C, the inactive metabolite of SIN-1, had no effect on [Ca2+](i). This study demonstrates that exogenously generated ONOO- modulates endothelial cell Ca2+ signaling, suggesting that ONOO- is of biological relevance to vasoregulation.