Mitochondrial ATP-sensitive potassium channels attenuate matrix Ca(2+) overload during simulated ischemia and reperfusion: possible mechanism of cardioprotection.
Mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels play a key role in ischemic preconditioning of the heart. However, the mechanism of cardioprotection remains controversial. We measured rhod-2 fluorescence in adult rabbit ventricular cardiomyocytes as an index of mitochondrial matrix Ca(2+) concentration ([Ca(2+)](m)), using time-lapse confocal microscopy. To simulate ischemia and reperfusion (I/R), cells were exposed to metabolic inhibition (50 minutes) followed by washout with control solution. Rhod-2 fluorescence gradually increased during simulated ischemia and rose even further with reperfusion. The mitoK(ATP) channel opener diazoxide attenuated the accumulation of [Ca(2+)](m) during simulated I/R (EC(50)=18 micromol/L). These effects of diazoxide were blocked by the mitoK(ATP) channel antagonist 5-hydroxydecanoate (5HD). In contrast, inhibitors of the mitochondrial permeability transition (MPT), cyclosporin A and bongkrekic acid, did not alter [Ca(2+)](m) accumulation during ischemia, but markedly suppressed the surge in rhod-2 fluorescence during reperfusion. Measurements of mitochondrial membrane potential, DeltaPsi(m), in permeabilized myocytes revealed that diazoxide depolarized DeltaPsi(m) (by 12% at 10 micromol/L, P<0.01) in a 5HD-inhibitable manner. Our data support the hypothesis that attenuation of mitochondrial Ca(2+) overload, as a consequence of partial mitochondrial membrane depolarization by mitoK(ATP) channels, underlies cardioprotection. Furthermore, mitoK(ATP) channels and the MPT differentially affect mitochondrial calcium homeostasis: mitoK(ATP) channels suppress calcium accumulation during I/R, while the MPT comes into play only upon reperfusion.
Murata
M
M
Institute of Molecular Cardiobiology, The Johns Hopkins University, Baltimore, MD, USA.
Akao
M
M
O'Rourke
B
B
Marbán
E
E
D001865:Bongkrekic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002469:Cell Separation; D019610:Cytoprotection; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D006880:Hydroxy Acids / Q000494:pharmacology; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D019194:Ischemic Preconditioning; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D017202:Myocardial Ischemia / Q000378:metabolism*; D015425:Myocardial Reperfusion; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010539:Permeability / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism
D003652:Decanoic Acids; D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D006880:Hydroxy Acids; D008565:Membrane Proteins; D015221:Potassium Channels; C117780:mitochondrial K(ATP) channel; C068483:rhod-2; D001865:Bongkrekic Acid; C052853:5-hydroxydecanoic acid; D003981:Diazoxide; D002118:Calcium