Effect of lysophosphatidylcholine on K + transport in rat heavy gastric membranes enriched with (H +-K +)-ATPase

Abstract

K +-and ATP-dependent H +-accumulation in rat heavy gastric membrane vesicles enriched with (H +-K +)-ATPase was markedly stimulated by amphiphiles like lysophosphatidylcholine and Zwittergent 3–14 at concentrations of 10 −5 M. Their stimulatory effect was dependent on K +-concentration in the medium and was abolished by SCH 28,080, a specific inhibitor of (H +-K +)-ATPase. Lysophosphatidylcholine at the optimal dose (3 × 10 −5 M) showed dual effects on K +-dependent membrane functions; it stimulated the rate of K +-uptake by nearly 60%, but partially inhibited SCH 28,080-sensitive and K +-dependent ATP-hydrolysis (about 20% reduction). These data indicate that H +-pumping through (H +-K +)-ATPase in the inside-out gastric membrane vesicles was facilitated by the stimulatory effect of lysophosphatidylcholine on membrane K +-transport in spite of its partial inhibition of ATP-hydrolysis. It appears that the rate limitingstep for operation of the ATPase is the availability of K + ions in the luminal side of the pump. We propose that ionic amphiphiles may modulate K +-transport in rat heavy gastric membranes through specific interactions with the putative K +-transporter