Effect of intracellular magnesium on calcium extrusion by the plasma membrane calcium pump of intact human red cells

The Journal of Physiology
J E Raftos, V L Lew

Abstract

1. The effect of varying the concentration of intracellular magnesium on the Ca(2+)-saturated Ca(2+)-extrusion rate through the Ca2+ pump (phi max) was investigated in human red blood cells with the aid of the divalent cation ionophore A23187. The aim was to characterize the [Mg2+]i dependence of the Ca2+ pump in the intact cell. 2. The initial experimental protocol consisted of applying a high ionophore concentration to obtain rapid sequential Mg2+ and [45Ca]CaCl2 equilibration, prior to measuring phi max at constant internal [MgT]i by either the Co2+ block method or by ionophore removal. With this protocol, competition between Ca2+ and Mg2+ through the ionophore prevented Ca2+ equilibration at high [Mg2+]o. To provide rapid and comparable Ca2+ loads and maintain intracellular ATP within normal levels it was necessary to separate the Mg2+ and the Ca2+ loading-extrusion stages by an intermediate ionophore and external Mg2+ removal step, and to use different metabolic substrates during Mg2+ loading (glucose) and Ca2+ loading-extrusion (inosine) periods. 3. Intracellular Co2+ was found to sustain Ca2+ extrusion by the pump at subphysiological [Mg2+]i. Ionophore removal was therefore used to estimate the [Mg2+]i dependence of the ...Continue Reading

Citations

Sep 1, 1999·European Journal of Biochemistry·J E RaftosP W Flatman
Dec 25, 2004·Physiological Reviews·Virgilio L Lew, Robert M Bookchin
Aug 27, 2005·Cellular Physiology and Biochemistry : International Journal of Experimental Cellular Physiology, Biochemistry, and Pharmacology·Diana TetiLeonardo Romano
May 15, 2001·American Journal of Physiology. Cell Physiology·J E RaftosT Tiffert
Mar 10, 2001·The Journal of Laboratory and Clinical Medicine·T TiffertV L Lew
Sep 17, 2002·European Journal of Pharmacology·Akira IkariYasunobu Suketa

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