Bapty B W, Dai L J, Ritchie G, Canaff L, Hendy G N, Quamme G A
Department of Medicine, University of British Columbia, University Hospital, Koerner Pavilion, Vancouver, British Columbia, Canada V6T 1Z3.
Am J Physiol. 1998 Sep;275(3):F353-60. doi: 10.1152/ajprenal.1998.275.3.F353.
The distal convoluted tubule plays a significant role in renal magnesium conservation. An immortalized mouse distal convoluted tubule (MDCT) cell line has been extensively used to study the cellular mechanisms of magnesium transport in this nephron segment. MDCT cells possess an extracellular polyvalent cation-sensing mechanism responsive to Mg2+, Ca2+, and neomycin. The present studies determined the effect of Mg2+/Ca2+ sensing on hormone-mediated cAMP formation and Mg2+ uptake in MDCT cells. MDCT cells were Mg2+ depleted by culturing in Mg2+-free media for 16 h, and Mg2+ uptake was measured by microfluorescence after placing the depleted cells in 1.5 mM MgCl2. The mean rate of Mg2+ uptake was 164 +/- 5 nM/s in control MDCT cells. Activation of Mg2+/Ca2+ sensing with neomycin did not affect basal Mg2+ uptake (155 +/- 5 nM/s). We have previously reported that treatment of MDCT cells with either glucagon or arginine vasopressin (AVP) stimulated Mg2+ entry. In the present studies, the addition of extracellular Mg2+ or Ca2+ inhibited glucagon- and AVP-stimulated cAMP formation and Mg2+ uptake in concentration-dependent manner with half-maximal concentrations of approximately 1.5 and 3.0 mM, respectively. Exogenous cAMP or forskolin stimulated Mg2+ uptake in the presence of Mg2+/Ca2+ sensing activation. We infer from these studies that Mg2+/Ca2+-sensing mechanisms located in the distal convoluted tubule may play a role in control of distal magnesium absorption.
远端曲管在肾脏镁离子保留中起重要作用。一种永生化小鼠远端曲管（MDCT）细胞系已被广泛用于研究该肾单位段镁离子转运的细胞机制。MDCT细胞具有对Mg2 +、Ca2 +和新霉素有反应的细胞外多价阳离子传感机制。本研究确定了Mg2 + / Ca2 +传感对MDCT细胞中激素介导的cAMP形成和Mg2 +摄取的影响。通过在无Mg2 +培养基中培养16小时使MDCT细胞耗尽Mg2 +，将耗尽的细胞置于1.5 mM MgCl2中后，通过微荧光测量Mg2 +摄取。对照MDCT细胞中Mg2 +摄取的平均速率为164±5 nM / s。用新霉素激活Mg2 + / Ca2 +传感不影响基础Mg2 +摄取（155±5 nM / s）。我们之前报道过，用胰高血糖素或精氨酸加压素（AVP）处理MDCT细胞会刺激Mg2 +进入。在本研究中，添加细胞外Mg2 +或Ca2 +以浓度依赖方式抑制胰高血糖素和AVP刺激的cAMP形成和Mg2 +摄取，半最大浓度分别约为1.5和3.0 mM。在存在Mg2 + / Ca2 +传感激活的情况下，外源性cAMP或福斯高林刺激Mg2 +摄取。我们从这些研究中推断，位于远端曲管的Mg2 + / Ca2 +传感机制可能在控制远端镁离子吸收中起作用。
