Dai L J, Bapty B, Ritchie G, Quamme G A
Department of Medicine, University of British Columbia, Vancouver Hospital, Canada.
Am J Physiol. 1998 Feb;274(2):F328-35. doi: 10.1152/ajprenal.1998.274.2.F328.
Glucagon and arginine vasopressin (AVP) enhance renal magnesium conservation through actions within the loop of Henle and the distal tubule. Studies were performed on an immortalized mouse distal convoluted tubule (MDCT) cell line to characterize the cellular actions of these hormones on Mg2+ transport in this segment of the distal tubule. Glucagon and AVP increased cellular cAMP concentrations by about fivefold above basal levels in normal and Mg(2+)-depleted cells. Intracellular free Mg2+ concentration ([Mg2+]i) was determined on single MDCT cells using microfluorescence with mag-fura 2. To assess Mg2+ uptake, MDCT cells were first Mg2+ depleted (0.22 +/- 0.01 mM) by culturing in Mg(2+)-free media for 16 h and then placed in 1.5 mM MgCl2, and the [Mg2+]i was determined. [Mg2+]i returned to basal levels, 0.53 +/- 0.02 mM, with a mean refill rate, d([Mg2+]i/dt, of 164 +/- 5 nM/s. Both glucagon and AVP stimulated Mg2+ uptake into MDCT cells, 196 +/- 11 and 189 +/- 6 nM/s, respectively, at concentrations of 3 x 10(-7) M and 10(-7) M, respectively. Enhanced Mg2+ uptake for each of the hormones was concentration dependent and inhibited by the channel blocker, nifedipine. Hormone stimulation of Mg2+ entry was not dependent on protein synthesis. 8-Bromo-cAMP, 10(-4) M, enhanced Mg2+ uptake (225 +/- 13 nM/s), whereas phorbol esters were without effect. Finally, protein kinase A inhibition prevented glucagon and AVP stimulation of Mg2+ uptake, supporting the notion that the cAMP pathway is important as expected in the hormone action. These studies demonstrate that glucagon and AVP stimulate Mg2+ uptake in MDCT cells and suggest that these hormones act to control magnesium conservation in the convoluted segment of the distal tubule.
胰高血糖素和精氨酸加压素（AVP）通过在髓袢和远曲小管中的作用增强肾脏对镁的保留。对永生化小鼠远曲小管（MDCT）细胞系进行了研究，以表征这些激素对远曲小管该节段中Mg2+转运的细胞作用。在正常和Mg(2+)缺乏的细胞中，胰高血糖素和AVP使细胞内cAMP浓度比基础水平增加约五倍。使用mag-fura 2通过微荧光法在单个MDCT细胞上测定细胞内游离Mg2+浓度（[Mg2+]i）。为了评估Mg2+摄取，首先通过在无Mg(2+)培养基中培养16小时使MDCT细胞Mg2+缺乏（0.22±0.01 mM），然后置于1.5 mM MgCl2中，并测定[Mg2+]i。[Mg2+]i恢复到基础水平，即0.53±0.02 mM，平均再填充速率d([Mg2+]i/dt)为164±5 nM/s。胰高血糖素和AVP均刺激Mg2+摄取到MDCT细胞中，浓度分别为3×10(-7) M和10(-7) M时，摄取速率分别为196±11和189±6 nM/s。每种激素增强的Mg2+摄取均呈浓度依赖性，并被通道阻滞剂硝苯地平抑制。激素刺激Mg2+进入不依赖于蛋白质合成。10(-4) M的8-溴-cAMP增强了Mg2+摄取（225±13 nM/s），而佛波酯则没有作用。最后，蛋白激酶A抑制阻止了胰高血糖素和AVP对Mg2+摄取的刺激，支持了cAMP途径在激素作用中如预期的那样很重要的观点。这些研究表明，胰高血糖素和AVP刺激MDCT细胞摄取Mg2+，并表明这些激素在控制远曲小管曲段中镁的保留方面发挥作用。
