Lysophosphatidylcholine increases cytosolic calcium in ventricular myocytes by direct action on the sarcolemma

Lysophosphatidylcholine (LPC) accumulates in myocardial tissues during ischemia, and has toxic effects which may contribute to the arrhythmias and relaxation abnormalities that occur during acute ischemia. These effects of LPC may be mediated in part by calcium overload. To test this hypothesis, spontaneously contracting cultured embryonic chick ventricular myocytes were superfused with various concentrations of LPC (10, 50 and 100 microM) while effects on contractile motion (video motion detector) and changes in free intracellular calcium ion concentration ([Ca2+]i indo-1 fluorescence) were determined. At concentrations greater than or equal to 10 microM, a dose-related, time-dependent effect occurred after exposure to LPC, consisting of the development of contracture and marked elevation of [Ca2+]i. LPC also produced a dose-related, time-dependent inhibition of K+ uptake, indicating there was inhibition of the Na(+)-K+ ATPase Na+ pump. However, the LPC-induced increase in [Ca2+]i was not due to Na+ overload caused by inhibition of the Na(+)-K+ ATPase Na+ pump because superfusion with a zero-Na+ solution did not prevent an increase in [Ca2+]i after LPC exposure; and the increase in [Ca2+]i after exposure to LPC occurred too rapidly to be accounted for by Na+ pump inhibition. Removal of extracellular Ca2+ prevented the rise in [Ca2+]i, after exposure to LPC but treatment with verapamil failed to inhibit the increase in [Ca2+]i induced by LPC. We conclude that LPC produces contracture due to an increase [Ca2+]i. These effects are seen at concentrations of 10 microM and greater, are not due to altered Na(+)-K+ ATPase Na+ pump or calcium channel function, and are probably related to the detergent properties of this amphiphile. There effects may account in part for myocardial dysfunction during ischemia in intact tissue.