Characterization of Na(+)-dependent Mg2+ efflux from Mg2(+)-loaded rat erythrocytes.
Na(+)-dependent Mg2+ efflux from Mg2(+)-loaded rat erythrocytes was determined from the increase of extracellular Mg2+ concentration or decrease of intracellular Mg2+ content, as measured by means of atomic absorption spectrophotometry. Mg2+ efflux was specifically combined with the uptake of Na+ at a stoichiometric ratio of 2Na+:1Mg2+, indicating electroneutral Na+/Mg2+ antiport. Na+/Mg2+ antiport depended on intracellular ATP and was inhibited by amiloride and quinidine, but was insensitive to strophanthin. Net Mg2+ efflux was only occurring at increased concentration of intracellular Mg2+ ([Mg2+]i), and stopped when the physiological Mg2+ content was reached. Intracellular Mg2+ acted cooperatively with a Hill coefficient of 2.4, which may indicate gating of Na+/Mg2+ antiport at increased [Mg2+]i. At increased intracellular Na+ concentration, Na+ competed with intracellular Mg2+ for Mg2+ efflux and Na+ could leave the rat erythrocyte via this transport system. Na+/Mg2+ antiport was working asymmetrically with respect to extra- and intracellular Na+ and Mg2+, and did not perform net Mg2+ uptake.
Günther
T
T
Institute of Molecular Biology and Biochemistry, Free University, Berlin, Germany.
Vormann
J
J
Höllriegl
V
V
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000032:analysis / Q000502:physiology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000201:enzymology / Q000378:metabolism; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D007425:Intracellular Membranes / Q000032:analysis; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism* / Q000502:physiology; D011802:Quinidine / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*; D013054:Spectrophotometry, Atomic
D000584:Amiloride; D000255:Adenosine Triphosphate; D012964:Sodium; D000251:Adenosine Triphosphatases; D008274:Magnesium; D011802:Quinidine