Exercise training alters the Ca2+ and contractile responses of coronary arteries to endothelin

We tested the hypothesis that alterations in myoplasmic free Ca2+ (Ca(m)) regulation in coronary smooth muscle after exercise training (Ex) underlie changes in vasomotor function. Yucatan miniature pigs were endurance trained by treadmill running for 16-20 wk. Simultaneous determination of Ca(m) (fura-2 microfluorometry) and contraction during endothelin exposure in coronary arteries were then performed. Endothelin (10(-9) to 10(-7) M) was administered either cumulatively or as a single concentration. Ex significantly attenuated the Ca(m) response to 10(-9) and 10(-8) M endothelin. Developed tension was significantly diminished at 10(-8) M endothelin in Ex pigs, producing a rightward shift in the concentration-developed tension response. Attenuated Ca(m) and contractile response to 10(-8) M endothelin were present after Ex whether endothelin was applied cumulatively or as a single concentration. The developed tension-Ca(m) relationship showed an increased Ca(m) sensitivity of contraction with Ex. Endothelin (10(-8) M)-induced Ca2+ influx, estimated by Ba2+ influx in low-Na+ solution, was increased threefold in coronary arteries from Ex pigs. The decreased Ca(m) in the presence of increased divalent cation (i.e., Ca2+) influx during 10(-8) M endothelin suggests a greatly enhanced sarcolemmal Ca2+ cycling in coronary arteries from Ex pigs.