EXERCISE TRAINING ALTERS THE CA2-ARTERIES TO ENDOTHELIN( AND CONTRACTILE RESPONSES OF CORONARY)

We tested the hypothesis that alterations in myoplasmic free Ca2+ (Ca- m) regulation in coronary smooth muscle after exercise training (Ex) u nderlie changes in vasomotor function. Yucatan miniature pigs were end urance trained by treadmill running for 16-20 wk. Simultaneous determi nation of Ca-m (fura-2 microfluorometry) and contraction during endoth elin 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 diminish ed at 10(-8) M endothelin in Ex pigs, producing a rightward shift in t he concentration-developed tension response. Attenuated Ca-m and contr actile response to 10(-8) M endothelin were present after Ex whether e ndothelin was applied cumulatively or as a single concentration. The d eveloped tension-Ca-m relationship showed an increased Ca-m sensitivit y of contraction with Ex. Endothelin (10(-8) M)-induced Ca2+ influx, e stimated by Ba2+ influx in low-Na+ solution, was increased threefold i n coronary arteries from Ex pigs. The decreased Ca-m in the presence o f increased divalent cation (i.e., Ca2+) influx during 10(-8) M endoth elin suggests a greatly enhanced sarcolemmal Ca2+ cycling in coronary arteries from Ex pigs.