Pharmacological Discrimination of Plasmalemmal and Mitochondrial Sodium–Calcium Exchanger in Cardiomyocyte-Derived H9c2 Cells

We examined the effects of SEA0400 and CGP-37157 on the plasmalemmal Na+–Ca2+ exchanger (NCX) and mitochondrial NCX using H9c2 cardiomyocytes loaded with Ca2+-sensitive fluorescent probes. The plasmalemmal NCX activity, which was measured as the increase in cytoplasmic Ca2+ concentration after application of low Na+ extracellular solution, was inhibited by SEA0400 but not by CGP-37157. The mitochondrial NCX activity, which was measured in permeabilized H9c2 cells as the decrease in mitochondrial Ca2+ concentration after application of Ca2+-free extramitochondrial solution, was inhibited by CGP-37157 but not by SEA0400. These results indicate that SEA0400 and CGP-37157 act as selective inhibitors towards plasmalemmal and mitochondrial NCX, respectively, and provide pharmacological evidence that the plasmalemmal and mitochondrial NCX are distinct molecular entities.