Acidic Preconditioning Inhibits Na+/H+ and Na+/Ca2+ Exchanger Interaction via PKCε in Guinea-Pig Ventricular Myocytes

Abstract

An interaction between the Na+/Ca2+ exchanger (NCX) and the Na+/H+ exchanger (NHE) induces reperfusion injury. We investigated the effect of brief repetitive acidosis as acidic preconditioning on NCX and NHE interaction during recovery from acidosis. NCX current with the reversal potential was measured in guinea-pig ventricular myocytes using the whole-cell voltage clamp. The cells were exposed to 5 min of acidosis preceded by two episodes of brief acidosis as acidic preconditioning. Acidosis inhibited NCX current and upon recovery shifted its reversal potential in the negative direction. The shift was prevented by cariporide, but was augmented by a high concentration of phorbol 13-myristate acetate (PMA). Acidic preconditioning prevented the shift, but not in the presence of a selective PKCε inhibitor. A low concentration of PMA, which activates PKCε selectively, prevented the shift, but together with PKCå inhibitor (εV1-2) restored the shift during recovery. 5-Hydroxydecanoate inhibited the effects of acidic preconditioning and those of both low and high concentrations of PMA. The negative shift of NCX reversal potential during recovery from acidosis may be due to [Na+]i accumulation by the NHE. Acidic preconditioning prevented the shift most likely by activating PKCε, which in turn inhibited the NHE. The NHE–NCX interaction may be one of the important end-effectors of preconditioning. Keywords:: acidosis, preconditioning, Na+/Ca2+ exchanger, Na+/H+ exchanger, guinea-pig ventricular myocyte