Quantification of Mg2+ extrusion and cytosolic Mg2+-buffering in Xenopus oocytes.
Intracellular Mg(2+) buffering and Mg(2+) extrusion were investigated in Xenopus laevis oocytes. Mg(2+) or EDTA were pressure injected and the resulting changes in the intracellular Mg(2+) concentration were measured simultaneously with Mg(2+)-selective microelectrodes. In the presence of extracellular Na(+), injected Mg(2+) was extruded from the oocytes with an estimated v(max) and K(M) of 74 pmol cm(-2)s(-1) and 1.28 mM, respectively. To investigate genuine cytosolic Mg(2+) buffering, measurements were carried out in the nominal absence of extracellular Na(+) to block Mg(2+) extrusion, and during the application of CCCP (inhibiting mitochondrial uptake). Under these conditions, Mg(2+) buffering calculated after both MgCl(2) and EDTA injections could be described by a buffer equivalent with a concentration of 9.8mM and an apparent dissociation constant, K(d-app), of 0.6mM together with an [ATP](i) of 0.9 mM with a K(d-app) 0.12 mM. Xenopus oocytes thus possess highly efficient mechanisms to maintain their intracellular Mg(2+) concentration.
Gabriel
Thomas E
TE
Institut für Neurobiologie, Heinrich-Heine-Universität, Universitätsstrasse 1, 40225 Düsseldorf, Germany.
Günzel
Dorothee
D
D000818:Animals; D002138:Calibration; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000737:chemistry; D003600:Cytosol / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D008839:Microelectrodes; D009865:Oocytes / Q000378:metabolism*; D013500:Surface Tension; D014981:Xenopus
D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D008274:Magnesium