| Summary: | Using the whole-cell voltage clamp, we examined the mechanism of activation of the Na+/Ca2+ exchanger (NCX) by hydrogen peroxide (H2O2) in isolated guinea-pig cardiac ventricular myocytes. Exposure to H2O2 increased the NCX current. The effect was inhibited by cariporide, an inhibitor of the Na+/H+ exchanger (NHE), suggesting that there are NHE-dependent and -independent pathways in the effect of H2O2 on NCX. In addition, both pathways were blocked by edaravone, a hydroxyl radical (•OH) scavenger; pertussis toxin, a Gαi/o protein inhibitor; and U0126, an inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK). On the other hand, wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, inhibited only the NHE-dependent pathway, while PP2, a Src family protein tyrosine kinase inhibitor, inhibited only the NHE-independent pathway. Taken together, our data suggest that H2O2 increases the NCX current via two signal transduction pathways. The common pathway is the conversion of H2O2 to •OH, which activates Gαi/o protein and a mitogen-activated protein (MAP) kinase signaling pathway. Then, one pathway activates NHE with a PI3K-dependent mechanism and indirectly increases the NCX current. Another pathway involves activation of a Src family tyrosine kinase. Keywords:: Na+/Ca2+ exchanger (NCX), hydrogen peroxide (H2O2), Na+/H+ exchanger (NHE), cardiac myocyte
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