Lysophospholipids do not directly modulate Na⁺-H⁺ exchange

Abstract

Lysophosphatidylcholine (LPC) has been reported to stimulate Na⁺-H⁺ exchange in rat cardiomyocytes. This action may be important in pathological conditions like ischemic injury where LPC is generated and Na⁺-H⁺ exchange activation is an important determinant of cardiac damage and dysfunction. It is unclear, however, if this stimulation of Na⁺-H⁺ exchange by LPC occurs through a direct action on the exchanger or through stimulation of a second messenger pathway. The purpose of the present investigation was to determine if lysolipids could directly affect Na⁺-H⁺ exchange. Purified cardiac sarcolemmal membranes were isolated and Na⁺-H⁺ exchange was measured by radioisotopic methods following addition of LPC. There were no effects of LPC on Na⁺-H⁺ exchange at LPC concentrations of ≤ 100 μM at all reaction times examined. Lysophosphatidylethanolamine (LPE), lysophosphatidylserine (LPS), lysophosphatidylinositol (LPI) and lysoplasmenylcholine (LP_EC) also did not alter Na⁺-H⁺ exchange at all concentrations and reaction times examined. We conclude that any stimulatory effects of lysolipids on Na⁺-H⁺ exchange do not occur through a direct action on the exchanger or its membrane lipid environment and must occur through a second messenger pathway.