Autocrine Action and Its Underlying Mechanism of Nitric Oxide on Intracellular Ca super(2+) Homeostasis in Vascular Endothelial Cells

The rise in cytosolic Ca super(2+) concentration (Ca super(2+) sub(i)) in vascular endothelial cells (ECs) activates the production and release of nitric oxide (NO). NO modifies Ca super(2+) sub(i) homeostasis in many types of nonendothelial cells. However, its effect on endothelial Ca super(2+) sub(i) homeostasis at basal and excited states remains unclear. In the present study, to elucidate the effect of NO on basal Ca super(2+) sub(i), inositol 1,4,5-trisphosphate-induced Ca super(2+) sub(i) release (IICR) was blocked by expressing an antisense against type-1 inositol 1,4,5-trisphosphate receptors or by microinjecting heparin to individual ECs, and the effects of NO that was released by and diffused from adjacent IICR-intact ECs were recorded. After ATP or bradykinin stimulation, IICR-inhibited ECs showed a marked reduction of basal Ca super(2+) sub(i), which was abolished by N super(G)-monomethyl-L-arginine monoacetate pretreatment. The reduction disappeared in sparsely seeded ECs. Exogenous NO gas mimicked the effect of ATP or bradykinin to reduce basal Ca super(2+) sub(i). Blocking plasma membrane Ca super(2+)-ATPase (PMCA), but not Na super(+)-Ca super(2+) exchange or sarcoplasmic/endoplasmic reticulum Ca super(2+)-ATPase, suppressed the reduction, indicating that the reduction resulted from a NO-dependent potentiation of PMCA. To elucidate the effect of NO on elevated Ca super(2+) sub(i), ATP-, bradykinin-, or thapsigargin-evoked Ca super(2+) sub(i) response in the presence and absence of NO production was compared in adjacent IICR-intact ECs. NO was found to potentiate PMCA, which, in turn, greatly attenuated agonist- evoked Ca super(2+) sub(i) elevation. NO also potentiated Ca super(2+) influx, which markedly increased the sustained phase of Ca super(2+) sub(i) elevation and possibly NO production. NO did not affect other Ca super(2+) sub(i)-elevating and Ca super(2+) sub(i)-sequestrating components. Thus, NO-dependent potentiation of PMCA is crucial for Ca super(2+) sub(i) homeostasis over a wide Ca super(2+) sub(i) range.