A mitochondrial uncoupler increases KCa currents but decreases KV currents in pulmonary artery myocytes.
Intracellular free Ca2+ concentration ([Ca2+]i) and ATP play important roles in the regulation of K- channels in pulmonary artery (PA) myocytes. Previous studies have demonstrated that hypoxia and the metabolic inhibitor, 2-deoxy-D-glucose, decrease voltage-gated K+ (KV) currents [IK(V)] and thereby depolarize PA myocytes; these effects lead to a rise in [Ca2+]i. Here, we used carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone (FCCP), a protonophore that uncouples mitochondrial respiration from ATP production, to test whether the inhibition of oxidative phosphorylation affects K+ channel activities in rat PA myocytes. Patch-clamp and fluorescent-imaging microscopy techniques were used to measure K+ currents (IK) and [Ca2+]i, respectively. FCCP (3-5 microM) reversibly raised [Ca2-]i in the presence and absence of external Ca2+. This effect was prevented by pretreating the cells with the membrane-permeable Ca2+ chelator, 1,2-bis(2-amino-phenoxy) ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA-AM). This suggests that much of the FCCP-evoked rise in [Ca2-]i was due to Ca2+ release from intracellular stores. Brief exposure to FCCP (approximately 2 min) reversibly enhanced Ik. This augmentation was not influenced by glibenclamide, an ATP-sensitive K channel blocker, but was eliminated by pretreatment with BAPTA-AM. This implies that the FCCP-evoked rise in [Ca2+]i activated Ca(2+)-activated K- (Kca) channels. Furthermore, in BAPTA-treated cells, longer application (> or = 6 min) of FCCP reversibly decreased IK(V) in PA cells bathed in Ca(2+)-free solution. These results demonstrate that FCCP affects KCa and Kv channels by different mechanisms. FCCP increases IK[Ca] by raising [Ca2+]i primarily as a result of Ca2+ release, but decreases IK(V) by a Ca(2+)-independent mechanism, presumably the inhibition of oxidative ATP production.
Yuan
X J
XJ
Department of Medicine, University of Maryland School of Medicine, Baltimore, USA.
Sugiyama
T
T
Goldman
W F
WF
Rubin
L J
LJ
Blaustein
M P
MP
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology*; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004553:Electric Conductivity; D007425:Intracellular Membranes / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D009994:Osmolar Concentration; D011188:Potassium / Q000502:physiology*; D011651:Pulmonary Artery / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D014475:Uncoupling Agents / Q000494:pharmacology*
D014475:Uncoupling Agents; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D004533:Egtazic Acid; D011188:Potassium; D002118:Calcium