THE AMILORIDE-SENSITIVE NA+/H+ EXCHANGE SYSTEM IN SKELETAL-MUSCLE CELLS IN CULTURE

Google Scholar
  • 1 January 1982
    • journal article
    • research article
    • Vol. 257  (16) , 9394-9400
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 7.5-8.5. The Vmax 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 Kd for amiloride is 5 .mu.M in Na+-free conditions and is constant between pH 7.5-8.5. 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.