An impurity in xanthine oxidase increases endothelin binding to pig coronary artery smooth muscle

Since endothelin (ET) is a potent vasoconstrictor and the free radicals are produced in ischemia-reperfusion, we determined the effect of superoxide on ET-1 binding to its receptors. Microsomes from pig coronary artery smooth muscle contained mostly ETa- and some ETb -receptors. Initially, we used xanthine oxidase (XO) purified from bovine milk + 0.3 mM xanthine (X) to generate superoxide. We pretreated the microsomes with X, XO, or X + XO to …