An ouabain-insensitive Na-ATPase of the arterial vascular muscle cell and its relation to ouabain-sensitive Na,K-ATPase.

A Na+-stimulated, Mg++-requiring ATPase (Na-ATPase), which is insensitive to ouabain, has been demonstrated in the carotis and coronary arteries of different species. In dependence on the sodium concentration half-maximal activities of Na-ATPase are found in the range from 16 to 24 mM Na+. A replacement of Mg++ by Ca++ leads to a partial loss of activity. It does not, however, change its sensitivity to sodium. Compared to Na,K-ATPase, the Na-ATPase shows a considerably lower sensitivity to calcium. p-Chloro-mercuribenzoate, N-ethylmaleinimide, chloropromazine, sodium fluoride, ethanol and sodium azide influence the activity of the Na-ATPase in a characteristic way corresponding to the reactivity of Na,K-ATPase. Noradrenaline and isoprenaline do not lead to any significant change of its activity. The possible separate existence of a Na-ATPase independent of Na,K-ATPase, as well as its potential importance for cellular metabolism are discussed.