Na+-K+-ATPase in vascular smooth muscle.

Na+-K+-ATPase has been isolated and characterized from canine aortic tissue. The ouabain-sensitive enzyme activity was 24 mumol X mg protein-1 X h-1, and the remaining Mg2+-ATPase activity was 54 mumol X mg protein-1 X h-1. The ratio of Na+-K+-ATPase to ouabain-sensitive K+-phosphatase was 13 to 1, similar to other more homogeneous preparations from other tissues. The dissociation characteristics of the enzyme-glycoside complex of this aortic preparation were the same as for cardiac preparations in that it was stabilized by K+. These data suggest that the nature of both the ATP hydrolytic site of Na+-K+-ATPase and the ouabain binding site are the same in preparations from vascular smooth muscle as in preparations from other tissues.