INHIBITION OF NA+ AND K+ STIMULATED ATPASE ACTIVITY OF RABBIT AND DOG HEART SARCOLEMMA BY LYSOPHOSPHATIDYL CHOLINE

Lysophosphatidylcholine (LPC) added at 30 μM or 10 μM to sarcolemma (SL) membranes of rabbit or dog causes about 50% inhibition of the Mg++ dependent Na+ + K+ stimulated ATPase activity. Higher concentration (100 μM) of free fatty acid (FFA) is needed to produce the same inhibition. Lysophosphatidyl ethanolamine, phosphorylcholine, phosphorylethanolamine also inhibit the enzyme activity. The inhibition of LPC is competitive for the Na+ site of the enzyme and it also affects the K+ site. The inhibitory effect of LPC is not additive to that produced by FFA or ouabain, on the contrary at low concentrations of these inhibitors the inhibition of LPC is reversed. The possible effects of increased levels of blood or tissue LPC on heart cell functions related to the Na+ + K+ ATPase activity are discussed. The possible interference of LPC with cardiac glycoside action is also discussed. © 1979.