Effects of SM-20550, a selective Na+-H+ exchange inhibitor, on the ion transport of myocardial mitochondria

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• 作者：Hotta ; Yoshihiro ; Ishikawa ; Naohisa ; Ohashi ; Naohito ; Matsui ; Kazuki
• 关键词：mitochondria ; Na+ ; H+ ; Na+Ca2+ exchange ; fluorometry ; Ca2+ overload ; N ; (aminoiminomethyl) ; 1 ; 4 ; dimethyl ; 1H ; indole ; 2 ; carboxamide methanesulfonate (SM ; 20550) ; 5 ; (N ; ethyl ; N ; isopropyl) amiloride hydrochloride (EIPA)
• 刊名：Molecular and Cellular Biochemistry
• 出版年：2001
• 出版时间：2001
• 年：2001
• 卷：219
• 期：1/2
• 页码：83-90
• 全文大小：187 KB

文摘

The effect of a novel Na$^+$-H$^+$ exchange inhibitor, SM-20550 [N-(aminoiminomethyl)-1,4-dimethyl-1H-indole-2-carboxamide methanesulfonate] (SM) on the ion transport of myocardial mitochondria was studied using ion fluorometry and superfusion techniques. Isolated mitochondria from the guinea-pig heart were pre-loaded with fluoroprobes of either BCECF AM for H$^+$, SBFI AM for Na$^+$ or fura-2 AM for Ca$^2+$. Initially, the treated mitochondria were superfused with a normal medium (MOPS-buffer, pH 7.4, 24°C), subsequently fluorometric experiments on the Na$^+$, H$^+$, Ca$^2+$ mobilization across the mitochondrial membrane were performed. The intramitochondrial pH (pH$\_m$) was increased by the superfusion of Na$^+$ at physiological cytosolic concentrations of 10 mM, indicating the existence of a Na$^+$-H$^+$ exchange in mitochondrial membranes. The Na$^+$ induced elevation of pH$\_m$ was dose-dependently inhibited by SM 1 &mgr;M (&Dgr;pH$\_m$; 45% as drug-free 100%), and 10 &mgr;M (&Dgr;pH$\_m$; 70%(, as observed in our experiments with the myocardial sarcolemmal membrane. The selective Na$^+$-H$^+$ exchange inhibitor SM reduced such pH$\_m$ elevations more markedly than that of EIPA [5-(N-ethyl-N-isopropyl) amiloride]. The Na$^+$-H$^+$ exchange inhibitors, SM and EIPA suppressed the intramitochondrial Ca$^2+$ elevation ([Ca$^2+$]$\_m$) brought on by external Ca$^2+$ concentration changes: The pretreatment with SM 1 &mgr;M, 10 &mgr;M and EIPA 10 &mgr;M reduced the [Ca$^2+$]$\_m$ influx by 28.3, 56.5 and 63%, respectively. Additionally, the [Ca$^2+$]$\_m$ elevation induced by acidification of the perfusate was reduced by the prior infusion of SM and EIPA. Pretreatment of mitochondria with SM or EIPA which had beneficial effects on the left ventricular developed pressure (LVDP) in the ischemia-reperfusion injury of Langendorff hearts, reduced the intramitochondrial Na$^+$ and pH$\_m$ levels, indicating interplay of the inhibitory mechanism of Ca$^2+$-uptake into mitochondria coupled with Na$^+$-H$^+$ exchange. These findings suggested that protective effects of Na$^+$-H$^+$ exchange inhibitors on reperfused myocardium are due in part to the Ca$^2+$-paradox at the mitochondria level.