Dai L J, Ritchie G, Bapty B, Quamme G A
Department of Medicine, University of British Columbia, Vancouver Hospital and Health Sciences Centre, Canada.
Am J Physiol. 1998 Feb;274(2):F336-41. doi: 10.1152/ajprenal.1998.274.2.F336.
The distal convoluted tubule reabsorbs significant amounts of filtered magnesium that is under hormonal control. In this study, we describe the effects of aldosterone on Mg2+ uptake in an immortalized mouse distal convoluted tubule (MDCT) cell line. Intracellular free Mg2+ concentration ([Mg2+]i) was determined on single MDCT cells using microfluorescence with mag-fura 2. To determine Mg2+ entry rate into MDCT cells, they were first Mg2+ depleted ([Mg2+]i, 0.22 +/- 0.01 mM) by culturing in Mg(2+)-free media for 16 h and then placed in 1.5 mM MgCl2. The rate of change in [Mg2+]i as measured as a function of time, d([Mg2+]i)/dt, was 164 +/- 5 nM/s in control cells. We have shown that glucagon or arginine vasopressin (AVP) stimulates Mg2+ entry by 63% and 15%, respectively. Incubation of MDCT cells with aldosterone for 16 h did not change the rate of Mg2+ uptake (172 +/- 8 nM/s). However, aldosterone potentiated glucagon- and AVP-stimulated Mg2+ uptake rate up to 330 +/- 39 and 224 +/- 6 nM/s, respectively. Aldosterone also potentiated glucagon- and AVP-induced intracellular cAMP accumulation in a concentration-independent manner. As cAMP stimulates Mg2+ entry in MDCT cells, it is inferred that aldosterone may stimulate Mg2+ uptake through intracellular signaling pathways involving cAMP. The actions of aldosterone were dependent on de novo protein synthesis, as pretreatment of the cells with cycloheximide inhibited aldosterone potentiation of hormone stimulation of Mg2+ uptake and cAMP accumulation. These studies with MDCT cells suggest that aldosterone may modulate the effects of hormones acting within the distal convoluted tubule to control magnesium absorption.
远曲小管重吸收大量经滤过的镁，且该过程受激素控制。在本研究中，我们描述了醛固酮对永生化小鼠远曲小管（MDCT）细胞系中镁离子摄取的影响。使用镁荧光指示剂fura 2通过微荧光法测定单个MDCT细胞内的游离镁离子浓度（[Mg2+]i）。为了确定镁离子进入MDCT细胞的速率，首先将细胞在无镁培养基中培养16小时使其镁离子耗尽（[Mg2+]i为0.22±0.01 mM），然后置于1.5 mM MgCl2中。在对照细胞中，[Mg2+]i随时间变化的速率d([Mg2+]i)/dt为164±5 nM/s。我们已经表明，胰高血糖素或精氨酸加压素（AVP）分别刺激镁离子进入增加63%和15%。将MDCT细胞与醛固酮孵育16小时并未改变镁离子摄取速率（172±8 nM/s）。然而，醛固酮分别将胰高血糖素和AVP刺激的镁离子摄取速率增强至330±39和224±6 nM/s。醛固酮还以浓度无关的方式增强了胰高血糖素和AVP诱导的细胞内cAMP积累。由于cAMP刺激MDCT细胞中的镁离子进入，可以推断醛固酮可能通过涉及cAMP的细胞内信号通路刺激镁离子摄取。醛固酮的作用依赖于从头合成蛋白质，因为用环己酰亚胺预处理细胞会抑制醛固酮对激素刺激的镁离子摄取和cAMP积累的增强作用。这些对MDCT细胞的研究表明，醛固酮可能调节作用于远曲小管内以控制镁吸收的激素的作用。
