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

Abstract

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 μM) decreased [Ca2+]i, whereas higher concentrations (50 or 100 μM) increased [Ca2+]i persistently. Further experiments demonstrated that pretreatment of ASMCs with calcium-free medium completely abolished [Ca2+]i increase by 100 μM 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.