Temporal responses to intrinsically coupled calcium and zinc dyshomeostasis in cardiac myocytes and mitochondria during aldosteronism

Abstract

Intracellular Ca2+overloading, coupled to induction of oxidative stress, is present at 4-wk aldosterone/salt treatment (ALDOST). This prooxidant reaction in cardiac myocytes and mitochondria accounts for necrotic cell death and subsequent myocardial scarring. It is intrinsically linked to increased intracellular zinc concentration ([Zn2+]i) serving as an antioxidant. Herein, we addressed the temporal responses in coupled Ca2+and Zn2+dyshomeostasis, reflecting the prooxidant-antioxidant equilibrium, by examining preclinical ( week 1) and pathological ( week 4) stages of ALDOST to determine whether endogenous antioxidant defenses would be ultimately overwhelmed to account for this delay in cardiac remodeling. We compared responses in cardiomyocyte free [Ca2+]iand [Zn2+]iand mitochondrial total [Ca2+]mand [Zn2+]m, together with biomarkers of oxidative stress and antioxidant defenses, during 1- and 4-wk ALDOST. At week 1 and compared with controls, we found: 1) elevations in [Ca2+]iand [Ca2+]mwere coupled with [Zn2+]iand [Zn2+]m; 2) increased mitochondrial H2O2production, cardiomyocyte xanthine oxidase activity, and cardiac and mitochondrial 8-isoprostane levels, counterbalanced by increased activity of antioxidant proteins, enzymes, and the nonenzymatic antioxidants that can be considered as cumulative antioxidant capacity; some of these enzymes and proteins (e.g., metallothionein-1, Cu/Zn-superoxide, glutathione synthase) are regulated by metal-responsive transcription factor-1; and 3) although these augmented antioxidant defenses were sustained at week 4, they fell short in combating the persistent intracellular Ca2+overloading and marked rise in cardiac tissue 8-isoprostane and mitochondrial transition pore opening. Thus a coupled Ca2+and Zn2+dyshomeostasis occurs early during ALDOST in cardiac myocytes and mitochondria that regulate redox equilibrium until week 4 when ongoing intracellular Ca2+overloading and prooxidants overwhelm antioxidant defenses.