Abstract
ATP-sensitive K+ (KATP) channels are present on the sarcolemma (sarcKATP channels) and mitochondria (mitoKATP channels) of cardiac myocytes. Amiodarone, a class III antiarrhythmic drug, reduces sudden cardiac death in patients with organic heart disease. The objective of the present study was to investigate the effects of amiodarone on sarcKATP and mitoKATP channels. Single sarcKATP channel current and flavoprotein fluorescence were measured in guinea pig ventricular myocytes to assay sarcKATP and mitoKATP channel activity, respectively. Amiodarone inhibited the sarcKATP channel currents in a concentration-dependent manner without affecting its unitary amplitude. The IC50 values were 0.35 μM in the inside-out patch exposed to an ATP-free solution and 2.8 μMin the cell-attached patch under metabolic inhibition, respectively. Amiodarone (10 μM) alone did not oxidize the flavoprotein. In addition, the oxidative effect of the mitoKATP channel opener diazoxide (100 μM) was unaffected by amiodarone. Exposure to ouabain (1 mM) for 30 min produced mitochondrial Ca2+ overload, and the intensity of rhod-2 fluorescence increased to 246 ± 16% of baseline (n = 9). Amiodarone did not alter the ouabain-induced mitochondrial Ca2+ overload (236 ± 10% of baseline, n = 7). Treatment with diazoxide significantly reduced the ouabain-induced mitochondrial Ca2+ overload (158 ± 15% of baseline, n = 8, p < 0.05 versus ouabain); this effect was not abolished by amiodarone (154 ± 10% of baseline, n = 8, p < 0.05 versus ouabain). These results suggest that amiodarone inhibits sarcKATP but not mitoKATP channels in cardiac myocytes. Such an action of amiodarone may effectively prevent ischemic arrhythmias without causing ischemic damage.
Footnotes
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This study was supported in part by grants-in-aid for scientific research, the Mitsui Life Social Welfare Foundation, and the Mochida Memorial Foundation for Medical and Pharmaceutical Research.
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ABBREVIATIONS: KATP, ATP-sensitive potassium; sarcKATP, sarcolemmal KATP; mitoKATP, mitochondrial KATP; HMR 1883, 1-[[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl]-3-methylthiourea; 5HD, 5-hydroxydecanoate; DNP, 2,4-dinitrophenol; Po, probability of opening; [Ca2+]m, mitochondrial Ca2+ concentration.
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DOI: 10.1124/jpet.103.055863.
- Received June 17, 2003.
- Accepted August 7, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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