EFFECT OF PALMITYLCARNITINE ON OUABAIN BINDING TO NA, K-ATPASE

Palmitylcarnitine, an endogenous long-chain fatty acyl ester, inhibited cardiac Na, K-ATPase activity and binding of [3H]ouabain to the enzyme. The inhibitory effects on enzyme hydrolytic activity and drug binding were time and concentration dependent, but also dependent upon the ratio of palmitylcarnitine to protein. Palmitylcarnitine inhibitory effects were irreversible, but could be prevented by bovine serum albumin. In the presence of Mg2+ + ATP or Mg2+ + Pi, [3H]ouabain binding was fully inhibited by 100 μm palmitylcarnitine. The addition of sodium, or sodium plus potassium to the drug-binding medium reduced the inhibitory effect. The protective action of Na+ was concentration dependent and was optimal at 75 μm palmitylcarnitine. Equimolar amounts of choline chloride did not have the same protective effect as sodium chloride. Binding of ouabain to the enzyme in the absence of palmitylcarnitine prevented the protective effect of Na+. Inhibition of Na, K-ATPase functional properties occurred at a concentration range of palmitylcarnitine reported to occur in the cytosol of ischemic cells during episodes of experimental myocardial ischemia. It is suggested that elevated levels of palmitylcarnitine in ischemic myocardium may play a role in altering cellular function as well as the inotropic response of ischemic cardiac muscle to digitalis glycosides. © 1979.