Characterization of Na+-dependent phosphate transport in cardiac sarcolemmal vesicles.

摘要: Pi uptake by purified bovine cardiac sarcolemmal vesicles was stimulated an inwardly directed Na+ gradient, but not such gradients of K+, Rb+, Li+, and choline. When present both inside outside the vesicles, or when gradient dissipated monensin, Na+-dependent increased with time, reached a peak, then declined approaching steady state. The initial rate saturable function concentration (Km = 0.5 mM). These findings indicate existence Na+,Pi-cotransporter in sarcolemma. Na+-activation curve exhibited positive cooperativity, suggesting requirement for multiple binding to functional unit carrier. decreased as extra-vesicular pH range 5.5-8.7. under conditions that are known expected generate inside-negative membrane potential, indicating is accompanied charge. results suggest electrogenic cotransports two one H2PO4-. We conclude this cotransporter catalyzes secondary active transport across plasma regulates myocardial energy metabolism. also may control intracellular thus be involved regulation trans-sarcolemmal Ca2+ movement contractility.