Sarcolemmal and mitochondrial effects of a KATP opener, P-1075, in "polarized" and "depolarized" Langendorff-perfused rat hearts.
We investigated consequences of cardiac arrest on sarcolemmal and mitochondrial effects of ATP-sensitive potassium channel (KATP) opener, P-1075, in Langendorff-perfused rat hearts. Depolarised cardiac arrest (24.7 mM KCl) did not affect glibenclamide-sensitive twofold activation of rubidium efflux by P-1075 (5 microM) from rubidium-loaded hearts, but eliminated uncoupling produced by P-1075 in beating hearts: 40% depletion of phosphocreatine and ATP, 50% increase in oxygen consumption, and reduction of cytochrome c oxidase. Depolarized cardiac arrest by calcium channel blocker, verapamil (5 microM), also prevented uncoupling. Lack of P-1075 mitochondrial effects in depolarized hearts was not due to changes in phosphorylation potential, because 2,4-dintrophenol (10 microM) reversed the [PCr]/[Cr] increase and Pi decrease, characteristic of KCl-arrest, but did not restore uncoupling. In agreement with this conclusion, pyruvate (5 mM) increased [PCr]/[Cr] and decreased Pi, but did not prevent uncoupling in beating hearts. A decrease in mean [Ca2+] in KCl-arrested hearts could not account for lack of P-1075 mitochondrial effects, because calcium channel opener, S-(-)-Bay K8644 (50 nM), and beta-agonist, isoproterenol (0.5 microM), did not facilitate uncoupling. In contrast, in adenosine (1 mM)-arrested hearts (polarized arrest), P-1075 caused 40% phosphocreatine and ATP depletion. In isolated rat liver mitochondria, P-1075 (20 microM) decreased mitochondrial membrane potential (DeltaPsi) by approximately 14 mV (demonstrated by redistribution of DeltaPsi-sensitive dye, rhodamine 800) in a glibenclamide-sensitive manner. We concluded that cell membrane depolarization does not prevent activation of sarcolemmal KATP by P-1075, but it plays a role in mitochondrial uncoupling effects of P-1075.
Jilkina
Olga
O
Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, MB, Canada.
Kuzio
Bozena
B
Grover
Gary J
GJ
Folmes
Clifford D L
CD
Kong
Hee-Jeong
HJ
Kupriyanov
Valery V
VV
D000818:Animals; D006146:Guanidines / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects*; D006324:Heart Arrest, Induced; D008099:Liver / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D008928:Mitochondria / Q000187:drug effects*; D011188:Potassium / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012413:Rubidium / Q000378:metabolism; D012508:Sarcolemma / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology*
D006146:Guanidines; D011725:Pyridines; D014665:Vasodilator Agents; C073896:N-cyano-N'-(1,1-dimethylpropyl)-N''-(3-pyridinyl)guanidine; D012413:Rubidium; D011188:Potassium