Sorcin modulates mitochondrial Ca2+ handling and reduces apoptosis in neonatal rat cardiac myocytes

Abstract

Sorcin localizes in cellular membranes and has been demonstrated to modulate cytosolic Ca2+ handling in cardiac myocytes. Sorcin also localizes in mitochondria; however, the effect of sorcin on mitochondrial Ca2+ handling is unknown. Using mitochondrial pericam, we measured mitochondrial Ca2+ concentration and fluxes in intact neonatal cardiac myocytes overexpressing sorcin. Our results showed that sorcin increases basal and caffeine-stimulated mitochondrial Ca2+ concentration. This effect was associated with faster Ca2+ uptake and release. The effect of sorcin was specific for mitochondria, since similar results were obtained with digitonin-permeabilized cells, where cytosolic Ca2+ flux was disrupted. Furthermore, mitochondria of cardiac myocytes in which sorcin was overexpressed were more Ca2+-tolerant. Experiments analyzing apoptotic signaling demonstrated that sorcin prevented 2-deoxyglucose-induced cytochrome c release. Furthermore, sorcin prevented hyperglycemia-induced cytochrome c release and caspase activation. In contrast, antisense sorcin induced caspase-3 activation. Thus, sorcin antiapoptotic properties may be due to modulation of mitochondrial Ca2+ handling in cardiac myocytes.