title: SM-20550, a new Na+/H+ exchange inhibitor and its cardioprotective effect in ischemic/reperfused isolated rat hearts by preventing Ca2+-overload.
abstract: We investigated the effect of a newly synthesized compound, SM-20550 [N-(aminoiminomethyl)-1,4-dimethyl-1H-indole-2-carboxamide methanesulfonic acid] on Na+/H+ or Na+/Ca2+ exchange activity in rat cardiomyocytes, and on radioligand binding with several channels or receptors in membrane preparations, and ischemia/reperfusion injury in isolated perfused rat hearts. In myocytes, SM-20550 concentration-dependently inhibited the recovery from acidosis induced by an NH4Cl prepulse in HCO3(-)-free solution. Its IC50 was 10(-8) M, which was 10 times lower than that of ethylisopropyl amiloride (EIPA). SM-20550 (10(-6) M) did not affect the Na+-dependent Ca2+ influx (Na+/Ca2+ exchange activity) in cardiomyocytes. In the radioligand binding assay, SM-20550 did not have affinity for K+ channel, beta-adrenoceptor, adenosine, angiotensin, or endothelin receptors, and had low affinity for Na+ and Ca2+ channels and alpha-adrenoceptors, only at the concentrations of 10(-6)-10(-5) M. In perfused hearts exposed to 40 min of global ischemia and 20 min of reperfusion, SM-20550 (10(-8)-10(-7) M) significantly reduced the elevation of left ventricular end-diastolic pressure during reperfusion, improved the postischemic recovery of developed pressure, and prevented coronary perfusion pressure increase after reperfusion. Furthermore, SM-20550 reduced creatine phosphokinase release during reperfusion and prevented the abnormal gain of tissue Na+ and Ca2+ at the end of reperfusion. These results suggest that SM-20550 is a potent, highly specific Na+/H+ exchange inhibitor, which exerts a protective effect against myocardial ischemia/reperfusion injury. In addition, our data strongly support the hypothesis that Na+/H+ exchange plays an important role in the development of postischemic cardiac dysfunction, most likely by inducing Na+ and Ca2+ overload.
authors.affiliation: Research Center, Sumitomo Pharmaceuticals Co., Ltd., Osaka, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Yamamoto
authors.forename: K
authors.initials: K
authors.lastname: Matsui
authors.forename: M
authors.initials: M
authors.lastname: Kitano
authors.forename: N
authors.initials: N
authors.lastname: Ohashi
mesh_terms: D000578:Amidines / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D017202:Myocardial Ischemia; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D011941:Receptors, Adrenergic / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013997:Time Factors
chemical_list: D000578:Amidines; D015220:Calcium Channels; D007211:Indoles; D011941:Receptors, Adrenergic; C121094:SM 20550; D017923:Sodium-Hydrogen Exchangers; D002118:Calcium