Altered cardiac Na+/H+ exchange in phospholipase D-treated sarcolemmal vesicles

Cardiac sarcolemmal Na+/H+ exchange is critical for the regulation of intracellular pH, and its activity contributes to ischemia-reperfusion injury. It has been suggested that the membrane phospholipid environment does not modulate Na+/H+ exchange. The present study was carried out to determine the effects on Na+/H+ exchange of modifying the endogenous membrane phospholipids through the addition of exogenous phospholipase D. Incubation of 0.825 U of phospholipase D with 1 mg of porcine cardiac sarcolemmal vesicles hydrolyzed 34 +/- 2% of the sarcolemmal phosphatidylcholine and increased phosphatidic acid 10.2 +/- 0.5-fold. Treatment of vesicles with phospholipase D resulted in a 46 +/- 2% inhibition of Na+/H+ exchange. Na+/H+ exchange was measured as a function of reaction time, extravesicular pH, and extravesicular Na+. All of these parameters of Na+/H+ exchange were inhibited following phospholipase D treatment compared with untreated controls. Passive efflux of Na+ was unaffected. Treatment of sarcolemmal vesicles with phospholipase C had no effect on Na+/H+ exchange. We conclude that phospholipase D-induced changes in the cardiac sarcolemmal membrane phospholipid environment alter Na+/H+ exchange.