Ca<SUP>2+</SUP>-dependent Long-term Inactivation of Cardiac Na<SUP>+</SUP>/Ca<SUP>2+</SUP> Exchanger

Ca<SUP>2+</SUP>-dependent Long-term Inactivation of Cardiac Na<SUP>+</SUP>/Ca<SUP>2+</SUP> Exchanger

Using BHK cells with stable expression of cardiac Na<SUP>+</SUP>/Ca<SUP>2+</SUP> exchanger (BHK-NCX1), reverse mode (i.e. Ca<SUP>2+</SUP> influx mode) of NCX1 current was recorded by whole-cell patch clamp. Repeated stimulation of reverse NCX1 produced a cytosolic Ca<SUP>2+</SUP>-dependent long-term inactivation of the exchanger activity. The degrees of inactivation correlated with NCX1 densities of the cells and were attenuated by reduced Ca<SUP>2+</SUP> influx via the reverse exchanger. The inactivation of NCX1 was attenuated by (i) inhibition of Ca<SUP>2+</SUP> influx with reduced extracellular Ca<SUP>2+</SUP>, (ii) treatment with NCX1 blocker (Ni<SUP>2+</SUP>), and (iii) increase of cytoplasmic Ca<SUP>2+</SUP> buffer (EGTA). In BHK-NCX1 cells transiently expressing TRPV1 channels, Ca<SUP>2+</SUP> influx elicited by capsaicin produced a marked inactivation of NCX1. We suggest that cytoplasmic Ca<SUP>2+</SUP> has a dual effect on NCX1 activities, and that allosteric Ca<SUP>2+</SUP> activation of NCX1 can be opposed by the Ca<SUP>2+</SUP>-dependent long-term inactivation in intact cells.