Uncoupling the Coupled Calcium and Zinc Dyshomeostasis in Cardiac Myocytes and Mitochondria Seen in Aldosteronism

Intracellular [Ca2+](i) overloading in cardiomyocytes is a fundamental pathogenic event associated with chronic aldosterone/salt treatment (ALDOST) and accounts for an induction of oxidative stress that leads to necrotic cell death and consequent myocardial scarring. This prooxidant response to Ca2+ overloading in cardiac myocytes and mitochondria is intrinsically coupled to simultaneous increased Zn2+ entry serving as an antioxidant. Herein, we investigated whether Ca2+ and Zn2+ dyshomeostasis and prooxidant to antioxidant dysequilibrium seen at 4 weeks, the pathologic stage of ALDOST, could be uncoupled in favor of antioxidants, using cotreatment with a ZnSO4 supplement; pyrrolidine dithiocarbamate (PDTC), a Zn2+ ionophore; or ZnSO4 in combination with amlodipine (Amlod), a Ca2+ channel blocker. We monitored and compared responses in cardiomyocyte free [Ca2+](i) and [Zn2+](i) together with biomarkers of oxidative stress in cardiac myocytes and mitochondria. At week 4 of ALDOST and compared with controls, we found (1) an elevation in [Ca2+](i) coupled with [Zn2+](i) and (2) increased mitochondria. H2O2 production and increased mitochondrial and cardiac 8-isoprostane levels. Cotreatment with the ZnSO4 supplement alone, PDTC, or ZnSO4+Amlod augmented the rise in cardiomyocyte [Zn2+](i) beyond that seen with ALDOST alone, whereas attenuating the rise in [Ca2+](i), which together served to reduce oxidative stress. Thus, a coupled dyshomeostasis of intracellular Ca2+ and Zn2+ was demonstrated in cardiac myocytes and mitochondria during 4-week ALDOST, where prooxidants overwhelm antioxidant defenses. This intrinsically coupled Ca2+ and Zn2+ dyshomeostasis could be uncoupled in favor of antioxidant defenses by selectively increasing free [Zn2+](i) and/or reducing [Ca2+](i) using cotreatment with ZnSO4 or PDTC alone or ZnSO4+Amlod in combination.