title: Amiodarone inhibits sarcolemmal but not mitochondrial KATP channels in Guinea pig ventricular cells.
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 microM in the inside-out patch exposed to an ATP-free solution and 2.8 microM in the cell-attached patch under metabolic inhibition, respectively. Amiodarone (10 microM) alone did not oxidize the flavoprotein. In addition, the oxidative effect of the mitoKATP channel opener diazoxide (100 microM) was unaffected by amiodarone. Exposure to ouabain (1 mM) for 30 min produced mitochondrial Ca(2+) overload, and the intensity of rhod-2 fluorescence increased to 246 +/- 16% of baseline (n = 9). Amiodarone did not alter the ouabain-induced mitochondrial Ca(2+) overload (236 +/- 10% of baseline, n = 7). Treatment with diazoxide significantly reduced the ouabain-induced mitochondrial Ca(2+) 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.
authors.affiliation: Department of Pharmacology, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan. tsato@faculty.chiba-u.jp
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Sato
authors.forename: Taichi
authors.initials: T
authors.lastname: Takizawa
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Saito
authors.forename: Satoru
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Yukio
authors.initials: Y
authors.lastname: Hara
authors.forename: Haruaki
authors.initials: H
authors.lastname: Nakaya
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000465:Algorithms; D000638:Amiodarone / Q000494:pharmacology*; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology; D005420:Flavoproteins / Q000378:metabolism; D005453:Fluorescence; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D054086:KATP Channels; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D012414:Rubidium Radioisotopes; D012508:Sarcolemma / Q000187:drug effects*
chemical_list: D018528:ATP-Binding Cassette Transporters; D000889:Anti-Arrhythmia Agents; D005420:Flavoproteins; D054086:KATP Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012414:Rubidium Radioisotopes; C092520:uK-ATP-1 potassium channel; D010042:Ouabain; D000638:Amiodarone; D002118:Calcium