Mobilization of intracellular calcium by peroxynitrite in arteriolar smooth muscle cells from rats

The present study was designed to investigate the possible effects of peroxynitrite (ONOO-) on the intracellular calcium concentration ([Ca2+](i)) of mesenteric arteriolar smooth muscle cells (ASMCs), and to reveal the underlying mechanisms by using fluorescence imaging analysis. The results showed that ONOO- could exert a concentration- and time-dependent but also a dual effect on [Ca2+](i). Bolus administration with a low concentration of ONOO- (25 muM) decreased [Ca2+](i), whereas higher concentrations (50 or 100 muM) increased [Ca2+](i) persistently. Further experiments demonstrated that pretreatment of ASMCs with calcium-free medium completely abolished [Ca2+](i) increase by 100 muM ONOO-. Additionally, nifedipine, an antagonist of selective L-type voltage-gated calcium channels (VGCCs), delayed the [Ca2+](i) response to ONOO-, and ryanodine, an inhibitor of intracellular calcium release from the sarcoplasmic reticulum, effectively antagonized [Ca2+](i) increase during the late stage of ONOO- exposure. Furthermore, [Ca2+](i) alteration by ONOO- appeared to be intimately associated with the subsequent membrane potential changes. Although the mechanisms by which ONOO- alters [Ca2+](i) are complex, we conclude that a series of variables such as external calcium influx, activation of VGCCs, intracellular calcium release, and membrane potential changes are involved. The decrease of [Ca2+](i) in ASMCs by a low concentration of ONOO- may participate in the pathogenesis of low vasoreactivity in shock, and the increase of [Ca2+](i) by high concentrations of ONOO- may lead to calcium overload with cellular injury.