title: Nicorandil attenuates the mitochondrial Ca2+ overload with accompanying depolarization of the mitochondrial membrane in the heart.
abstract: The anti-anginal drug nicorandil has been demonstrated to protect the myocardium against ischemic injury in both experimental and clinical studies. Although nicorandil seems to protect the myocardium via activation of mitochondrial ATP-sensitive K+ (mitoKATP) channels, the mechanisms underlying its cardioprotection have remained elusive. We therefore examined whether nicorandil depolarizes the mitochondrial membrane and attenuates the mitochondrial Ca2+ overload. With the use of a Nipkow confocal system, the mitochondrial Ca2+ concentration ([Ca2+]m) and the mitochondrial membrane potential (DeltaPsim) in rat ventricular myocytes were measured by loading cells with rhod-2 and JC-1 respectively. The number of cell hypercontractures resulting from mitochondrial Ca2+ overload was counted. Exposing cells to ouabain (1 mM) evoked mitochondrial Ca2+ overload and increased the intensity of rhod-2 fluorescence to 180+/-15% of baseline ( p<0.001). Nicorandil (100 microM) significantly attenuated the ouabain-induced mitochondrial Ca2+ overload (129+/-4% of baseline; p<0.001 vs. ouabain). Nicorandil decreased the DeltaPsim during application of ouabain, thereby reducing the intensity of JC-1 fluorescence to 89+/-2% of baseline ( p<0.05). Exposure of myocytes to ouabain eventually resulted in cell hypercontracture (51+/-2%). This ouabain-induced cell hypercontracture was blunted by application of nicorandil (37+/-2%, p<0.05 vs. ouabain). Moreover, these effects of nicorandil were abolished by 5-hydroxydecanoate (500 microM), a putative mitoKATP channel blocker, and by glibenclamide (10 microM), a nonselective KATP channel blocker. Our results suggest that nicorandil attenuates the matrix Ca2+ overload with accompanying depolarization of the mitochondrial membrane. Such effect might potentially be attributed to the mechanism of cardioprotection afforded by nicorandil.
authors.affiliation: Department of Physiology, Tokai University School of Medicine, Isehara, Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Ishida
authors.forename: Naoko
authors.initials: N
authors.lastname: Higashijima
authors.forename: Yuki
authors.initials: Y
authors.lastname: Hirota
authors.forename: Chokoh
authors.initials: C
authors.lastname: Genka
authors.forename: Hiroe
authors.initials: H
authors.lastname: Nakazawa
authors.forename: Haruaki
authors.initials: H
authors.lastname: Nakaya
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Sato
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003652:Decanoic Acids / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology; D006880:Hydroxy Acids / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D020108:Nicorandil / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D003652:Decanoic Acids; D006880:Hydroxy Acids; D026902:Potassium Channel Blockers; D014665:Vasodilator Agents; D020108:Nicorandil; D010042:Ouabain; C052853:5-hydroxydecanoic acid; D000255:Adenosine Triphosphate; D005905:Glyburide; D002118:Calcium