Terikalant, an inward-rectifier potassium channel blocker, does not abolish the cardioprotection induced by ischemic preconditioning in the rat.
Recent results have shown that the sulfonylurea receptor couples to several types of inward-rectifier potassium (KIR) channels, which suggests that sensitivity to blockade of a pathophysiological phenomenon such as ischemic preconditioning (PC) by glibenclamide may not be the result of this compound selectively blocking the ATP-sensitive potassium (KATP) channel. Therefore, to address this possibility, a role for myocardial KIR v KATP channels in ischemic PC was evaluated in the rat. To test this hypothesis, anesthetized, open-chest, male Wistar rats were assigned to one of seven experimental protocols. Animals assigned to group I (control) received 30 min of occlusion and 2 h of reperfusion. Ischemic PC was produced by 3x5-min occlusion and 2-h reperfusion periods (group II). Terikalant (TK), an inward-rectifier potassium channel blocker, was used to test the role of other K+ channels, most notably the KIR, in the cardioprotective effect of ischemic PC in the rat. TK was given at a dose of 3 mg/kg, i.v., 15 min before the prolonged occlusion and reperfusion periods (group III). In groups IV, V, and VI terikalant (1, 3 and 6 mg/kg, i.v.) was given 15 min before ischemic PC (lowTK+PC, medTK+PC and hiTK+PC, respectively). Group VII consisted of glibenclamide (0.3 mg/kg, i.v.) given 30 min prior to ischemic PC (GLY+PC). Infarct size (IS) as a percent of the area at risk (AAR) was measured using the histochemical stain, 2,3, 5-triphenyltetrazolium chloride. The average IS/AAR for the control was 49.9+/-2.1%. Ischemic PC markedly reduced infarct size (8.6+/-1. 8%; * P<0.05 v control). Terikalant (TK; 1, 3 and 6 mg/kg, i.v.) did not abolish the cardioprotective effect of ischemic PC at any dose (15.5+/-6.4, 16.4+/-5.2 and 8.8+/-1.6%, respectively; * P<0.05 v control). TK itself had no effect on infarct size. GLY completely abolished the cardioprotective effect of ischemic PC (48.2+/-6.4%). In addition, the high dose of TK significantly (P<0.05) increased the action potential duration at 50% repolarization from 48+/-3 to 64+/-4 ms and 30 microM of TK, a concentration which produced a 39% decrease in the inward-rectifier potassium channel current in isolated guinea-pig ventricular myocytes in the whole-cell patch-clamp mode did not block the increase in K ATP current produced by the KATP opener bimakalim (3 microM). These results demonstrate that although the myocardial KATP channel belongs to the K IR superfamily, the endogenous myocardial KIR channel does not mediate ischemic PC in the rat heart; however, the K ATP channel does mediate its cardioprotective effect.
Schultz
J E
JE
Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, WI, 53226, USA.
Kwok
W M
WM
Hsu
A K
AK
Gross
G J
GJ
D018528:ATP-Binding Cassette Transporters; D000200:Action Potentials; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D002478:Cells, Cultured; D002839:Chromans / Q000494:pharmacology*; D004594:Electrophysiology; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006439:Hemodynamics; D019157:Ischemic Preconditioning, Myocardial; D054086:KATP Channels; D008297:Male; D009203:Myocardial Infarction / Q000503:physiopathology; D010880:Piperidines / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D051381:Rats; D017208:Rats, Wistar
D018528:ATP-Binding Cassette Transporters; D000889:Anti-Arrhythmia Agents; D002839:Chromans; D054086:KATP Channels; D010880:Piperidines; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; C092520:uK-ATP-1 potassium channel; C063899:terikalant