The direct physiological effects of mitoK(ATP) opening on heart mitochondria.
The mitochondrial ATP-sensitive K+ channel (mitoK(ATP)) has been assigned multiple roles in cell physiology and in cardioprotection. Each of these roles must arise from basic consequences of mitoK(ATP) opening that should be observable at the level of the mitochondrion. MitoK(ATP) opening has been proposed to have three direct effects on mitochondrial physiology: an increase in steady-state matrix volume, respiratory stimulation (uncoupling), and matrix alkalinization. Here, we examine the evidence for these hypotheses through experiments on isolated rat heart mitochondria. Using perturbation techniques, we show that matrix volume is the consequence of a steady-state balance between K+ influx, caused either by mitoK(ATP) opening or valinomycin, and K+ efflux caused by the mitochondrial K+/H+ antiporter. We show that increasing K+ influx with valinomycin uncouples respiration like a classical uncoupler with the important difference that uncoupling via K+ cycling soon causes rupture of the outer mitochondrial membrane and release of cytochrome c. By loading the potassium binding fluorescent indicator into the matrix, we show directly that K+ influx is increased by diazoxide and inhibited by ATP and 5-HD. By loading the fluorescent probe BCECF into the matrix, we show directly that increasing K+ influx with either valinomycin or diazoxide causes matrix alkalinization. Finally, by comparing the effects of mitoK(ATP) openers and blockers with those of valinomycin, we show that four independent assays of mitoK(ATP) activity yield quantitatively identical results for mitoK(ATP)-mediated K+ transport. These results provide decisive support for the hypothesis that mitochondria contain an ATP-sensitive K+ channel and establish the physiological consequences of mitoK(ATP) opening for mitochondria.
Costa
Alexandre D T
AD
Dept. of Biology, Portland State Univ., PO Box 751, Portland, OR 97207, USA.
Quinlan
Casey L
CL
Andrukhiv
Anastasia
A
West
Ian C
IC
Jabůrek
Martin
M
Garlid
Keith D
KD
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001572:Benzofurans; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D004988:Ethers, Cyclic; D006863:Hydrogen-Ion Concentration; D006880:Hydroxy Acids / Q000494:pharmacology; D008027:Light; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects / Q000502:physiology*; D008933:Mitochondrial Swelling / Q000187:drug effects; D009861:Onium Compounds / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000494:pharmacology; D010101:Oxygen Consumption; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012542:Scattering, Radiation; D014475:Uncoupling Agents / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
D001572:Benzofurans; D003652:Decanoic Acids; D004988:Ethers, Cyclic; D006880:Hydroxy Acids; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D015221:Potassium Channels; D014475:Uncoupling Agents; C117780:mitochondrial K(ATP) channel; C073886:potassium-binding benzofuran isophthalate; D014634:Valinomycin; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; C052853:5-hydroxydecanoic acid; D000255:Adenosine Triphosphate; D003981:Diazoxide; D011188:Potassium; C013289:tetraphenylphosphonium