IMR Press / FBL / Volume 9 / Issue 2 / DOI: 10.2741/1274

Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.

Article

Fluorometric evidence for different stoichiometries for the Na+/Mg2+ exchange in Mg-loaded rat thymocytes

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1 Departamento de Fisiología, Facultad de Medicina. Universidad de Granada. Avda Madrid 13 E-18012 Granada, Spain
2 Departamento de Farmacología, Facultad de Medicina, Universidad Nacional Autónoma de México, Ciudad Universitaria, CP 04510. Apartado Postal 70-297, México, D.F., México
3 Departamento de Farmacología, Facultad de Medicina, Universidad de Granada. Avda Madrid 13 E-18012 Granada, Spain
4 Instituto de Biotecnología, Universidad de Granada. Avda Madrid 13 E-18012 Granada, Spain
Front. Biosci. (Landmark Ed) 2004, 9(2), 1843–1848; https://doi.org/10.2741/1274
Published: 1 May 2004
Abstract

The regulation of the cytosolic free magnesium concentration ([Mg2+]i) is a fundamental cellular process that requires magnesium extruding mechanisms. Here, we present evidence indicating that rat thymocytes are endowed with different Na/Mg exchange systems. Fluxes of magnesium were measured using the fluorescent magnesium indicator magfura-2. Cells were loaded with magnesium using the calcium ionophore A-23187 to 0.6-8.0 mM [Mg2+]i (resting [Mg2+]i = 0.38 ± 0.06 mM, n = 5). The presence of extracellular sodium was required for magnesium exit. The initial rate of [Mg2+]i was stimulated by extracellular sodium with Michaelis-Menten kinetics. The Vmax of the sodium-dependent magnesium exit was markedly increased by [Mg2+]i. Holding the membrane potential at either –84 mV or at –10 mV had different effects on the sodium-stimulated magnesium efflux, depending on the extracellular sodium concentration ([Na+]o). At 10-30 mM [Na+]o, the magnesium efflux was faster at –10 mV than at –84 mV. Conversely, at 50-200 mM [Na+]o, the efflux of magnesium was faster at –84 mV that at –10 mV. At 75 mM [Na+]o, the activities where nearly the same at both membrane potential values. These observations suggest that the stochiometry of the Na+/Mg2+ exchange changes with [Na+]o.

Keywords
Intracellular magnesium
Na/Mg exchange
Mag Fura 2
Membrane Potential
Thymocytes
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