Role of Ca\(^{2+}\) in the Control of H\(_2\)O\(_2\)-Modulated Phosphorylation Pathways Leading to eNOS Activation in Cardiac Myocytes

Abstract

Nitric oxide (NO) and hydrogen peroxide (H\(_2\)O\(_2\)) play key roles in physiological and pathological responses in cardiac myocytes. The mechanisms whereby H\(_2\)O\(_2\)–modulated phosphorylation pathways regulate the endothelial isoform of nitric oxide synthase (eNOS) in these cells are incompletely understood. We show here that H\(_2\)O\(_2\) treatment of adult mouse cardiac myocytes leads to increases in intracellular Ca\(^{2+}\) ([Ca\(^{2+}\)]\(_i\)), and document that activity of the L-type Ca\(^{2+}\) channel is necessary for the H\(_2\)O\(_2\)-promoted increase in sarcomere shortening and of [Ca\(^{2+}\)]\(_i\). Using the chemical NO sensor Cu\(_2\)(FL2E), we discovered that the H\(_2\)O\(_2\)-promoted increase in cardiac myocyte NO synthesis requires activation of the L-type Ca\(^{2+}\) channel, as well as phosphorylation of the AMP-activated protein kinase (AMPK), and mitogen-activated protein kinase kinase 1/2 (MEK1/2). Moreover, H\(_2\)O\(_2\)-stimulated phosphorylations of eNOS, AMPK, MEK1/2, and ERK1/2 all depend on both an increase in [Ca\(^{2+}\)]\(_i\) as well as the activation of protein kinase C (PKC). We also found that H\(_2\)O\(_2\)-promoted cardiac myocyte eNOS translocation from peripheral membranes to internal sites is abrogated by the L-type Ca\(^{2+}\) channel blocker nifedipine. We have previously shown that kinase Akt is also involved in H\(_2\)O\(_2\)-promoted eNOS phosphorylation. Here we present evidence documenting that H\(_2\)O\(_2\)-promoted Akt phosphorylation is dependent on activation of the L-type Ca\(^{2+}\)channel, but is independent of PKC. These studies establish key roles for Ca\(^{2+}\)- and PKC-dependent signaling pathways in the modulation of cardiac myocyte eNOS activation by H\(_2\)O\(_2\).