Enhanced KCl-mediated contractility and Ca2+ sensitization in porcine collateral-dependent coronary arteries persist after exercise training

We have previously reported enhanced Ca2+ sensitivity of coronary arteries that is dependent upon collateral circulation for their blood supply. For the current study. we hypothesized that small collateral-dependent arteries would exhibit an enhanced KCl-mediated contractile response attributable to Ca2+ sensitization and increased Ca 2 + channel current. Ameroid constrictors were surgically placed around the left circumflex (LCX) artery of female Yucatan miniature swine. Eight weeks postoperatively, pigs were randomized into sedentary or exercise-trained (treadmill run; 5 days/wk; 14 wk) groups. Small coronary arteries (150-300 mu m luminal diameter) were isolated from myocardial regions distal to the collateral-dependent LCX and the nonoccluded left anterior descending arteries. Contractile tension and simultaneous measures of both tension and intracellular free Ca2+ levels (fura-2) were measured in response to increasing concentrations of KC1. In addition, whole cell Ca(2+ )currents were also obtained. Chronic occlusion enhanced contractile responses to KCl and increased Ca2+ sensitization in collateral-dependent compared with nonoccluded arteries of both sedentary and exercise-trained pigs. In contrast, smooth muscle cell Ca2+ channel current was not altered by occlusion or exercise training. Ca2+/calmodulin-dependent protein kinase II (CaMKII; inhibited by ICN-93. 0.3-1 mu M) contributed to the enhanced contractile response in collateral-dependent arteries of sedentary pigs, whereas both CaMKII and Rho-kinase (inhibited by hydroxyfasudil, 30 mu M or Y27632, 10 mu M) contributed to increased contraction in exercise-trained animals. Taken together, these data suggest that chronic occlusion leads to enhanced contractile responses to KCl in collateral-dependent coronary arteries via increased Ca2+ sensitization, a response that is further augmented with exercise training. NEW & NOTEWORTHY Small coronary arteries distal to chronic occlusion displayed enhanced contractile responses, which were further augmented after exercise training and attributable to enhanced calcium sensitization without alterations in calcium channel current. The calcium sensitization mediators Rho-kinase and CaMKII significantly contributed to enhanced contraction in collateral-dependent arteries of exercise-trained, but not sedentary, pigs. Exercise-enhanced contractile responses may increase resting arterial tone, creating an enhanced coronary flow reserve that is accessible during periods of increased metabolic demand.