Günther T, Vormann J, Höllriegl V
Institute of Molecular Biology and Biochemistry, Free University, Berlin, Germany.
Biochim Biophys Acta. 1990 Apr 30;1023(3):455-61. doi: 10.1016/0005-2736(90)90139-f.
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.
通过原子吸收分光光度法测量细胞外镁离子浓度的增加或细胞内镁离子含量的减少，来测定从负载镁离子的大鼠红细胞中钠依赖的镁离子外流。镁离子外流与钠离子摄取以2Na⁺:1Mg²⁺的化学计量比特异性结合，表明存在电中性的Na⁺/Mg²⁺反向转运体。Na⁺/Mg²⁺反向转运体依赖于细胞内ATP，并受到阿米洛利和奎尼丁的抑制，但对毒毛花苷不敏感。净镁离子外流仅在细胞内镁离子浓度（[Mg²⁺]i）增加时发生，并在达到生理镁离子含量时停止。细胞内镁离子协同作用，希尔系数为2.4，这可能表明在[Mg²⁺]i增加时Na⁺/Mg²⁺反向转运体的门控作用。在细胞内钠离子浓度增加时，钠离子与细胞内镁离子竞争镁离子外流，并且钠离子可以通过该转运系统离开大鼠红细胞。Na⁺/Mg²⁺反向转运体在细胞外和细胞内的钠离子和镁离子方面不对称运作，并且不进行净镁离子摄取。
