Exercise Training Restores K+ Channel Contributions to Hydrogen Peroxide-Mediated Dilation Independent of PKG Dimerization in Collateral-Dependent Coronary Arterioles
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In coronary artery disease (CAD), the ability of the coronary circulation to deliver blood to meet oxygen demands of the heart is often impaired. Exercise training has been established to mitigate the negative effects of CAD by preserving reactivity of the coronary microcirculation. We have previously reported that exercise increases the contribution of hydrogen peroxide (H2O2) to enhanced endotheliumdependent vasodilation in collateraldependent coronary arterioles. Others have shown that cGMPdependent protein kinase (PKG) can be activated via oxidation by H2O2, inducing dimer formation. The PKG dimer has been shown to act on substrates, such as K+ channels, to contribute to vascular smooth muscle relaxation and vasodilation. In the current study, we tested the hypothesis that exercise trainingenhanced H2O2induced vasodilation is mediated through enhanced PKG dimerization and subsequent activation of Kv and BKca channels in coronary arterioles isolated from ischemic myocardium. An ameroid occluder was surgically placed on the proximal left circumflex coronary artery of female Yucatan miniature swine to induce gradual occlusion while the left anterior descending artery was left unoccluded to serve as a control. Eight weeks postoperatively, pigs were assigned to sedentary (n=14) or exercise training (n=13; progressive treadmill training for 13 weeks) regimens. Coronary arterioles (75150 m) and small arteries (250400 um) were isolated from myocardium of the left circumflex and left anterior descending regions. Immunoblot analysis indicated that H2O2 induced PKG dimer formation in both porcine coronary arterioles and small arteries. Chronic coronary artery occlusion appeared to diminish H2O2mediated PKG dimer formation in collateraldependent arterioles and the reduced dimerization persisted with exercise training. H2O2mediated vasodilation tended to be impaired in arterioles isolated from the collateraldependent regions of sedentary pigs and was partially restored with exercise training. It also appears that both Kv and BKCa channels contributed to H2O2mediated dilation after exercise training. Our data demonstrate that H2O2 stimulates PKG dimer formation in both porcine coronary arterioles and small arteries. Contrary to our hypothesis, H2O2induced PKG dimerization is not enhanced by exercise training in either nonoccluded or collateraldependent arterioles. However, both Kv and BKCa channels appear to contribute to exercise trainingenhanced H2O2mediated dilation in collateraldependent coronary arterioles.Support or Funding InformationNational Institutes of Health R01HL139903
