title: The amiloride-sensitive Na+/H+ exchange system in skeletal muscle cells in culture.
abstract: Chick skeletal muscle cells in culture have an amiloride-sensitive Na+-transporting system that has the following properties. Na+ uptake is dependent on the extracellular Na+ concentration. The Km value for Na+ is 25 mM and remains constant between pH 7.5 and 8.5. The maximal rate of Na+ transport is higher at alkaline pH. An ionizable group with a pK of 7.6 is essential for the system to be functional. The activity of the amiloride-sensitive Na+ uptake system is controlled by internal Na+ and H+ concentrations. Amiloride inhibition of Na+ uptake is competitively antagonized by increasing Na+ concentration. The dissociation constant for amiloride is 5 microM in Na+-free conditions and is constant between pH 7.5 and 8.5. The Km value for Na+ found from competition experiments is 13 mM. The amiloride-sensitive Na+ influx occurs in parallel with an amiloride-sensitive H+ efflux. This H+ efflux is stimulated by increasing external Na+ concentrations, the Km for Na+ being 15 mM. It is inhibited by amiloride with the same concentration dependence as Na+ influx.
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D007700:Kinetics; D009132:Muscles / Q000196:embryology / Q000378:metabolism*; D011522:Protons; D011719:Pyrazines / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D011522:Protons; D011719:Pyrazines; D000584:Amiloride; D012964:Sodium