Earlier studies have shown that activation of
bradykinin B2 receptor triggers
protein kinase C (PKC)-mediated cardioprotective mechanism in ischemic preconditioning (PC). In the present study, we examined whether the effector in this B2-receptor triggered pathway of PC is the
ATP sensitive
potassium (K(
ATP)) channel in the mitochondria (mito-K(
ATP) channel) or K(
ATP) channel in the sarcolemma (sarc-K(
ATP) channel). Isolated rabbit hearts were perfused with modified
Krebs-Henseleit buffer in a Langendorff mode, and regional
myocardial ischemia was induced by occluding a left coronary artery for 30 min and then reperfusing for 2 hours.
Infarct size was determined by
triphenyltetrazolium chloride staining and expressed as a percentage of area at risk (% IS/AR). Infusion of
bradykinin (500 nmol/L) for 15 min prior to
ischemia significantly reduced % IS/AR from 37.4 +/- 2.9 (SE) of the untreated controls to 12.0 +/- 3.3%. This protective effect of
bradykinin was completely abolished by coinfusion of
5-hydroxydecanoate (5-HD, 50 micromol/L), a selective mito-K(
ATP) channel blocker (% IS/AR = 44.2 +/- 6.4). In contrast, a high dose of HMR1098 (20 micromol/L), which is a newly developed sarc-K(
ATP) channel selective blocker with IC50 of 0.6 micromol/L, failed to modify the
infarct size limitation by preischemic infusion of
bradykinin (% IS/AR = 11.7 +/- 3.4). Neither 5-HD nor HMR1098 alone modified
infarct size (% IS/AR = 37.8 +/- 3.8 and 35.1 +/- 6.2, respectively). These results suggest that opening of the mito-K(
ATP) channel but not the sarc-K(
ATP) channel is involved in
infarct size limitation by a mechanism triggered by
bradykinin B2 receptor activation.