Quantification of Mg²⁺ extrusion and cytosolic Mg²⁺-buffering in Xenopus oocytes

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• 作者：Thomas E. Gabriel ; Dorothee G&#xfc ; nzel
• 关键词：Xenopus laevis oocyte ; Leech Retzius neuron ; Magnesium ; ATP ; Buffering ; Na⁺/Mg²⁺ antiport ; Membrane transport
• 刊名：Archives of Biochemistry and Biophysics
• 出版年：2007
• 期刊代码：116_00039861
• 类别：ch
• 出版时间：1 February 2007
• 卷：458
• 期：1
• 页码：3-15
• 文件大小：430 K

摘要

Intracellular Mg²⁺ buffering and Mg²⁺ extrusion were investigated in Xenopus laevis oocytes. Mg²⁺ or EDTA were pressure injected and the resulting changes in the intracellular Mg²⁺ concentration were measured simultaneously with Mg²⁺-selective microelectrodes. In the presence of extracellular Na⁺, injected Mg²⁺ 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 Mg²⁺ buffering, measurements were carried out in the nominal absence of extracellular Na⁺ to block Mg²⁺ extrusion, and during the application of CCCP (inhibiting mitochondrial uptake). Under these conditions, Mg²⁺ buffering calculated after both MgCl₂ and EDTA injections could be described by a buffer equivalent with a concentration of 9.8 mM and an apparent dissociation constant, K_d-app, of 0.6 mM 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 Mg²⁺ concentration.