Kang H S, Kerstan D, Dai L J, Ritchie G, Quamme G A
Department of Medicine, University of British Columbia, Vancouver Hospital and Health Sciences Centre, Vancouver, British Columbia, Canada V6T 1Z3.
Am J Physiol Renal Physiol. 2000 Dec;279(6):F1116-23. doi: 10.1152/ajprenal.2000.279.6.F1116.
beta-Adrenergic agonists influence electrolyte reabsorption in the proximal tubule, loop of Henle, and distal tubule. Although isoproterenol enhances magnesium absorption in the thick ascending limb, it is unclear what effect, if any, beta-adrenergic agonists have on tubular magnesium handling. The effects of isoproterenol were studied in immortalized mouse distal convoluted tubule (MDCT) cells by measuring cellular cAMP formation with radioimmunoassays and Mg(2+) uptake with fluorescence techniques. Intracellular free Mg(2+) concentration (Mg(2+)) was measured in single MDCT cells by using microfluorescence with mag-fura-2. To assess Mg(2+) uptake, MDCT cells were first Mg(2+) depleted to 0.22 +/- 0.01 mM by culturing in Mg(2+)-free media for 16 h and then placed in 1.5 mM MgCl(2), and the changes in Mg(2+) were determined. Mg(2+) returned to basal levels, 0.53 +/- 0.02 mM, with a mean refill rate, d(Mg(2+))/dt, of 168 +/- 11 nM/s. Isoproterenol stimulated Mg(2+) entry in a concentration-dependent manner, with a maximal response of 252 +/- 11 nM/s, at a concentration of 10(-7) M, that represented a 50 +/- 7% increase in uptake rate above control values. This was associated with a sixfold increase in intracellular cAMP generation. Isoproterenol-stimulated Mg(2+) uptake was completely inhibited with RpcAMPS, a protein kinase A inhibitor, and U-73122, a phospholipase C inhibitor, and partially blocked by RO 31-822, a protein kinase C inhibitor. Accordingly, isoproterenol-mediated Mg(2+) entry rates involve multiple intracellular signaling pathways. Aldosterone potentiated isoproterenol-stimulated Mg(2+) uptake (326 +/- 31 nM/s), whereas elevation of extracellular Ca(2+) inhibited isoproterenol-mediated cAMP accumulation and Mg(2+) uptake, 117 +/- 37 nM/s. These studies demonstrate that isoproterenol stimulates Mg(2+) uptake in a cell line of mouse distal convoluted tubules that is modulated by hormonal and extracellular influences.
β-肾上腺素能激动剂影响近端小管、髓袢和远端小管中的电解质重吸收。尽管异丙肾上腺素可增强髓袢升支粗段对镁的吸收，但β-肾上腺素能激动剂对肾小管镁处理有何影响（若有影响的话）尚不清楚。通过放射免疫测定法测量细胞内环磷酸腺苷（cAMP）的生成，并采用荧光技术测量镁离子（Mg²⁺）摄取，研究了异丙肾上腺素对永生化小鼠远端曲小管（MDCT）细胞的影响。使用mag - fura - 2通过显微荧光法在单个MDCT细胞中测量细胞内游离镁离子浓度（[Mg²⁺]i）。为评估Mg²⁺摄取，先将MDCT细胞在无镁培养基中培养16小时，使其Mg²⁺浓度降至0.22±0.01 mM，然后置于1.5 mM MgCl₂中，测定[Mg²⁺]i的变化。[Mg²⁺]i恢复至基础水平，即0.53±0.02 mM，平均补充速率d([Mg²⁺]i)/dt为168±11 nM/s。异丙肾上腺素以浓度依赖的方式刺激Mg²⁺进入，在浓度为10⁻⁷ M时最大反应为252±11 nM/s，这表示摄取速率比对照值增加了50±7%。这与细胞内cAMP生成增加了六倍相关。异丙肾上腺素刺激的Mg²⁺摄取被蛋白激酶A抑制剂RpcAMPS和磷脂酶C抑制剂U - 73122完全抑制，并被蛋白激酶C抑制剂RO 31 - 822部分阻断。因此，异丙肾上腺素介导的Mg²⁺进入速率涉及多种细胞内信号通路。醛固酮增强了异丙肾上腺素刺激的Mg²⁺摄取（326±31 nM/s），而细胞外钙离子浓度升高则抑制了异丙肾上腺素介导的cAMP积累和Mg²⁺摄取，降至117±37 nM/s。这些研究表明，异丙肾上腺素刺激小鼠远端曲小管细胞系中的Mg²⁺摄取，且该过程受激素和细胞外因素的调节。
