Characterization of Na+/Mg2+ antiport by simultaneous 28Mg2+ influx.
During net Mg2+ efflux from Mg2+-preloaded chicken erythrocytes, which occurs via Na+/Mg2+ antiport, 28Mg2+ is taken up intracellularly. Km of 28Mg2+ influx amounted to 1 mM. In Na+-free medium Vmax of 28Mg2+ influx was increased and Km was reduced to 0.2 mM. 28Mg2+ influx was noncompetitively inhibited by amiloride as was found for Na+/Mg2+ antiport. The results indicate that, extracellularly, Mg2+ can compete with Na+ for common binding sites of the Na+/Mg2+ antiporter, resulting in 28Mg2+-24Mg2+ exchange. The rate of Mg2+ exchange depends on extracellular Na+ and on the rate of net Mg2+ efflux.
Institute of Molecular Biology and Biochemistry, Free University of Berlin, F.R.G.
T
T
Günther
J
J
Vormann
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002645:Chickens; D004910:Erythrocyte Membrane / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000097:blood*; D011188:Potassium / Q000097:blood; D012964:Sodium / Q000097:blood*
D000584:Amiloride; D012964:Sodium; D008274:Magnesium; D011188:Potassium