Exercise Training Rescues Impaired H 2 O 2 ‐Mediated Vasodilation in Collateral‐Dependent Coronary Arterioles Through Enhanced K + Channel Activation

Abstract

The objective of this study was to determine downstream cellular signaling pathways by which exercise training promotes H2O2-mediated dilation in arterioles distal to chronic coronary artery occlusion. We tested the hypothesis that exercise training would correct impaired H2O2-mediated dilation in collateral-dependent arterioles through enhanced coupling of H2O2 with voltage-gated K+ (Kv) and large-conductance, calcium-dependent K+ (BKCa) channels. Yucatan miniature swine were surgically instrumented with an Ameroid constrictor around the proximal left circumflex coronary artery, which gradually induced occlusion and created a collateral-dependent vascular bed. Arterioles from the left anterior descending artery region served as nonoccluded control vessels. Pigs were separated into two groups: one that underwent a progressive exercise training program (treadmill run; 5 days/week for 14 weeks) and another that remained sedentary and was limited to normal pen activity. Collateral-dependent arterioles from sedentary pigs were significantly less sensitive to H2O2-induced dilation compared with nonoccluded arterioles (EC50: -4.55 ± 0.15 vs. -4.91 ± 0.15 log M, respectively; P<0.05), whereas this difference was eliminated after completion of the exercise training regimen when collateral-dependent and nonoccluded arterioles responded similarly to H2O2 (EC50: -4.86 ± 0.16 vs. -4.95 ± 0.18 log M, respectively). H2O2-mediated dilation in nonoccluded or collateral-dependent arterioles from sedentary animals was not altered by inhibitors of Kv (4-aminopyridine; 1 mM) or BKCa (iberiotoxin; 100 nM) channels. In contrast, after exercise training, Kv channels contributed significantly to dilation in nonoccluded arterioles and both Kv and BKCa channels played a significant role in dilation of collateral-dependent arterioles. Interestingly, the contribution of Kv and BKCa channels to basal tone was not altered by occlusion or exercise training, suggesting similar availability of these channels in nonoccluded and collateral-dependent arterioles of sedentary and exercise-trained pigs. Immunoblot analysis was performed to assess levels of PKG dimerization, a potential mediator between H2O2 and K+ channels. These studies revealed that H2O2 treatment significantly increased PKG dimerization in all artery treatment groups, and this effect was significantly greater in nonoccluded compared with collateral-dependent arteries from sedentary pigs, but not different after exercise training. Taken together, our studies suggest that impaired H2O2-mediated vasodilation may be in part attributable to attenuated PKG dimerization in collateral-dependent arterioles of sedentary pigs. However, while exercise training appeared to correct impaired H2O2-mediated dilation via enhanced coupling to K+ channel activation, exercise-induced changes in PKG dimerization did not appear to play a role.