Peroxynitrite-Induced Intracellular Ca2+ Depression in Cardiac Myocytes: Role of Sarco/Endoplasmic Reticulum Ca2+...

Several studies have shown that peroxynitrite (ONOO-), formed upon the reaction of •NO and O2-, is increased in many cardiovascular diseases and is detrimental to myocardial function. Proteins associated with Ca2+ homeostasis regulation in the heart may be involved in these effects. Thus, the aim of this study was to elucidate the mechanisms associated with ONOO--induced effects. We evaluated [Ca2+]i regulation, sarco/endoplasmic reticulum Ca2+- binding proteins, and phosphorylation levels of the ryanodine receptor in isolated rat myocytes. Electrical field-induced intracellular Ca2+ transients and contractions were recorded simultaneously. Myocytes superfused with 3-morpholinosydnonimine N-ethylcarbamide (SIN-1), an ONOO- donor, decreased the amplitude of Ca2+ transients and contraction in a dose-response (1-200 μM) manner. Similarly, SIN-1 increased half-time decay in a concentration-dependent manner. Co-infusion of the ONOO- donor with FeTMPyP (1 μM), an ONOO- decomposition catalyst, inhibited the effects induced by ONOO-. Impaired sarcoplasmic reticulum Ca2+ uptake caused by ONOO- (SIN-1 200 μM) was confirmed by a reduction of caffeine-evoked Ca2+ release along with prolongation of the half-time decay. Surprisingly, ONOO- induced a spontaneous Ca2+ transient that started at the beginning of the relaxation phase and was inhibited by tetracaine. Also, reduced phosphorylation at the ryanodine receptor 2 (RyR2)-Ser-2814 site was observed. In conclusion, deficient sarco/endoplasmic reticulum Ca2+-ATPase-mediated Ca2+ uptake concomitant with augmented Ca2+ release by RyR2 in myocytes may be associated with modification of myocyte Ca2+ handling by ONOO-. Thus, development of cardiac failure in diabetes, nephropathy, or hypertension may be related with elevated ONOO- in cardiac tissue.