Na+Influx via Na+/H+Exchange Activates Protein Kinase C Isozymesδ and ϵ in Cultured Neonatal Rat Cardiac Myocytes

Abstract

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 [3H]phenylalanine incorporation, total protein content and β -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 [3H]phenylalanine incorporation. Staurosporine, a PKC inhibitor, completely abolished veratridine-induced hypertrophic response, but did not affect increment of intracellular Na+concentration by veratridine. PMA caused increases of α -, δ -and ϵ -PKC in the particulate fraction, but PE, ET-1 and veratridine affected only those of δ - and ϵ -PKC. HOE694 significantly inhibited only increases of δ - and ϵ -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.δ - and ϵ -PKC appear to be involved in the signal mechanism of the hypertrophic response induced by Na+influx through Na+/H+exchange in myocytes.