N-n-butyl haloperidol iodide inhibits H2O2-induced Na+/Ca2+-exchanger activation via the Na+/H+ exchanger in rat ventricular myocytes

N-n-butyl haloperidol iodide (F2), a novel compound, has shown palliative effects in myocardial ischemia/reperfusion (I/R) injury. In this study, we investigated the effects of F2 on the extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK)/Na(+)/H(+) exchanger (NHE)/Na(+)/Ca(2+) exchanger (NCX) signal-transduction pathway involved in H2O2-induced Ca(2+) overload, in order to probe the underlying molecular mechanism by which F2 antagonizes myocardial I/R injury. Acute exposure of rat cardiac myocytes to 100 μM H2O2 increased both NHE and NCX activities, as well as levels of phosphorylated MEK and ERK. The H2O2-induced increase in NCX current (I NCX) was nearly completely inhibited by the MEK inhibitor U0126 (1,4-diamino-2,3-dicyano-1,4-bis[o-aminophenylmercapto] butadiene), but only partly by the NHE inhibitor 5-(N,N-dimethyl)-amiloride (DMA), indicating the I NCX increase was primarily mediated by the MEK/mitogen-activated protein kinase (MAPK) pathway, and partially through activation of NHE. F2 attenuated the H2O2-induced I NCX increase in a concentration-dependent manner. To determine whether pathway inhibition was H2O2-specific, we examined the ability of F2 to inhibit MEK/ERK activation by epidermal growth factor (EGF), and NHE activation by angiotensin II. F2 not only inhibited H2O2-induced and EGF-induced MEK/ERK activation, but also completely blocked both H2O2-induced and angiotensin II-induced increases in NHE activity, suggesting that F2 directly inhibits MEK/ERK and NHE activation. These results show that F2 exerts multiple inhibitions on the signal-transduction pathway involved in H2O2-induced I NCX increase, providing an additional mechanism for F2 alleviating intracellular Ca(2+) overload to protect against myocardial I/R injury.