N-n-butyl haloperidol iodide inhibits H(2)O(2)-induced Na(+)/Ca(2+)-exchanger activation via the Na(+)/H(+) exchanger in rat ventricular myocytes

N-n-butyl haloperidol iodide (F(2)), a novel compound, has shown palliative effects in myocardial ischemia/reperfusion (I/R) injury. In this study, we investigated the effects of F(2) 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 H(2)O(2)-induced Ca(2+) overload, in order to probe the underlying molecular mechanism by which F(2) antagonizes myocardial I/R injury. Acute exposure of rat cardiac myocytes to 100 μM H(2)O(2) increased both NHE and NCX activities, as well as levels of phosphorylated MEK and ERK. The H(2)O(2)-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. F(2) attenuated the H(2)O(2)-induced I(NCX) increase in a concentration-dependent manner. To determine whether pathway inhibition was H(2)O(2)-specific, we examined the ability of F(2) to inhibit MEK/ERK activation by epidermal growth factor (EGF), and NHE activation by angiotensin II. F(2) not only inhibited H(2)O(2)-induced and EGF-induced MEK/ERK activation, but also completely blocked both H(2)O(2)-induced and angiotensin II-induced increases in NHE activity, suggesting that F(2) directly inhibits MEK/ERK and NHE activation. These results show that F(2) exerts multiple inhibitions on the signal-transduction pathway involved in H(2)O(2)-induced I(NCX) increase, providing an additional mechanism for F(2) alleviating intracellular Ca(2+) overload to protect against myocardial I/R injury.