Na+ influx via Na+/H+ exchange activates protein kinase C isozymes δ and ε in cultured neonatal rat cardiac myocytes

Protein kinase C (PKC) is one of the important signaling molecules in the development of the cardiac hypertrophic response, and activation of Na+/H+ exchange is caused by PKC in myocytes, In this study we examined the contribution of Na+/H+ exchange in cardiac hypertrophy induced by the activation of PKC and its mechanism using cultured neonatal rat cardiac myocytes. Phenylephrine (PE), endothelin-1 (ET-1) and phorbol 12-myristate 13-acetate (PMA) increased cytoplasmic pH in myocytes, and this effect was strongly inhibited by treatment with HOE694, an inhibitor of Na+/H+ exchange. These substances increased the [H-3]phenylalanine incorporation, total protein content and beta-myosin heavy chain protein content in myocytes. These hypertrophic responses were also attenuated by HOE694. To clarify the role of Na+ influx through activation of Na+/H+ exchange in cardiac hypertrophy, we next examined the hypertrophic responses to veratridine and ouabain, which increase the intracellular Na+ content. Veratridine and ouabain increased the [H-3]phenylalanine incorporation. Staurosporine, a PKC inhibitor, completely abolished veratridine-induced hypertrophic response, but did not affect increment of intracellular Nai concentration by veratridine. PMA caused increases of alpha-, delta- and epsilon-PKC in the particulate fraction, but PE, ET-1 and veratridine affected only those of delta- and epsilon-PKC, HOE694 significantly inhibited only increases of delta- and epsilon-PKC caused by PE, ET-1 or PMA, but not those by veratridine. These results demonstrate that Na+ influx via activation of Na+/H+ exchange reactivates PKC in myocytes. delta- and epsilon-PKC appear to be involved in the signal mechanism of the hypertrophic response induced by Na+ influx through Na+/H+ exchange in myocytes. (C) 1999 Academic Press.