Effects of palmitoyl carnitine and LPC on cardiac sarcolemmal Na+-K+-ATPase.

We have previously reported that palmitoyl carnitine is a potent inhibitor of Na+-K+-ATPase. Recently, Owens et al. [Am. J. Physiol. 242 (Heart Circ. Physiol. 11): H456-H461, 1983] reported that palmitoyl carnitine did not inhibit Na+-K+-ATPase activity of their cardiac sarcolemmal preparation that had been isolated without the use of detergents. We have investigated this using a similar preparation. Palmitoyl carnitine appears to be a much less effective inhibitor of the sarcolemmal preparation at lower concentrations because it simultaneously stimulates Na+-K+-ATPase by unmasking latent activity. When this latent activity is exposed by pretreatment with sodium dodecyl sulfate, a marked inhibition by palmitoyl carnitine is then observed. Similar results were obtained with lysophosphatidylcholine (LPC). The concentrations of palmitoyl carnitine and LPC required to inhibit Na+-K+-ATPase are, however, higher than those that cause sarcolemmal permeability changes; consequently, it is improbable that inhibition of the enzyme by these metabolites occurs to any significant extent in vivo.