Abstract
Chicken erythrocytes were loaded with Mg 2+ by incubation with the cation ionophore A 23187 in the presence of Mg 2+. After removing A 23187 by intensive washing with serum albumin and reincubating the Mg 2+-loaded cells, Mg 2+ was transported out of the cells until the original Mg 2+ content was achieved. The net Mg 2+ efflux followed Michaelis-Menten-kinetics and was independent of extracellular and intracellular Ca 2+ and calmodulin. The net Mg 2+ efflux was not affected by adrenalin, isoproterenol, p-chloromercuribenzenesulfonate, ouabain and tetrodotoxin, but was inhibited by dicyclohexylcarbodiimide, KCN, iodoacetate, high extracellular concentrations of Mg 2+, Mn 2+ and when extracellular Na + was substituted by choline or K +. The efflux of 1 Mg 2+ was coupled with the uptake of 2 Na +. It is concluded that there exists an additional gating process at the inner cell surface becoming active only at increased concentrations of intracellular free Mg 2+ regulating the exit of Mg 2+ by the efflux system.
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