二价阳离子调节肾近端小管细胞中甲状旁腺激素依赖性3',5'-环磷酸腺苷的产生。

Divalent cations modulate PTH-dependent 3',5'-cyclic adenosine monophosphate production in renal proximal tubular cells.

作者信息

Mathias R S, Brown E M

机构信息

Division of Nephrology, University of California, San Francisco 94143.

出版信息

Endocrinology. 1991 Jun;128(6):3005-12. doi: 10.1210/endo-128-6-3005.

DOI:10.1210/endo-128-6-3005

PMID:1645258

Abstract

The kidney and parathyroid gland play key roles in calcium (Ca++) homeostasis. Recent data suggest that the kidney, in addition to being a primary target for PTH, also recognizes changes in the concentration of extracellular Ca++, thereby modulating hormone-dependent cAMP production, 1,25-dihydroxyvitamin D synthesis, and renin secretion. In this study, we examined: 1) the effects of varying concentration of divalent cations on PTH-dependent cAMP production in renal proximal tubular cells; and 2) the mechanisms by which extracellular Ca++ exerts its inhibitory effects on cAMP production. Single cell suspensions composed of 80-90% proximal tubular cells were prepared from cortical homogenates by collagenase digestion and sieving. In the presence of 1 mM isobutylmethylxanthine, cAMP content was measured by RIA in 5-15 min incubations and showed a 5- to 6-fold increase in response to PTH (10(-11) -10(-6) M). Increasing extracellular Ca++ and magnesium (Mg++) from 0 and 0.5 mM, respectively, to 5.0 mM inhibited PTH-dependent (3 x 10(-9) M) cAMP production by 54 +/- 4% and 47 +/- 6%, respectively. The half maximal inhibitory concentration for both Ca++ and Mg++ was 0.9 mM. In addition, increasing extracellular barium (Ba++) or strontium (Sr++) from 0-10 mM inhibited PTH-dependent (3 x 10(-9) M) production by 54 +/- 7% and 62 +/- 6% with half of the maximal observed inhibition at 2.2 and 2.7 mM, respectively. The inhibition of PTH-dependent cAMP production by 2.5 mM Ca++ was not reversed by the calcium channel blockers diltiazem or verapamil (10(-4) M). However, changes in intracellular calcium may play some role in the inhibitory effects of Ca++ on cAMP production, since ionomycin (10(-6)-10(-5) M) lowered PTH-dependent cAMP production by 25-36%. Our data suggest that the proximal tubular cell can sense physiologically relevant changes in Ca++, providing a potential mechanism for the modulation of 1,25-dihydroxyvitamin D production or other tubular functions relevant to fluid and mineral homeostasis.

摘要

肾脏和甲状旁腺在钙（Ca++）稳态中发挥关键作用。近期数据表明，肾脏除了是甲状旁腺激素（PTH）的主要作用靶点外，还能感知细胞外Ca++浓度的变化，从而调节激素依赖性环磷酸腺苷（cAMP）的产生、1,25-二羟维生素D的合成以及肾素分泌。在本研究中，我们检测了：1）不同浓度二价阳离子对肾近端小管细胞中PTH依赖性cAMP产生的影响；2）细胞外Ca++对cAMP产生发挥抑制作用的机制。通过胶原酶消化和筛分从皮质匀浆中制备由80 - 90%近端小管细胞组成的单细胞悬液。在存在1 mM异丁基甲基黄嘌呤的情况下，通过放射免疫分析法（RIA）在5 - 15分钟孵育过程中测量cAMP含量，结果显示对PTH（10(-11) - 10(-6) M）的反应中cAMP含量增加了5至6倍。将细胞外Ca++和镁（Mg++）分别从0和0.5 mM增加到5.0 mM时，分别抑制PTH依赖性（3×10(-9) M）cAMP产生54±4%和47±6%。Ca++和Mg++的半数最大抑制浓度均为0.9 mM。此外，将细胞外钡（Ba++）或锶（Sr++）从0增加到10 mM时，分别抑制PTH依赖性（3×10(-9) M）cAMP产生54±7%和62±6%，最大抑制作用的半数分别在2.2 mM和2.7 mM时出现。2.5 mM Ca++对PTH依赖性cAMP产生的抑制作用不能被钙通道阻滞剂地尔硫䓬或维拉帕米（10(-4) M）逆转。然而，细胞内钙的变化可能在Ca++对cAMP产生的抑制作用中发挥一定作用，因为离子霉素（10(-6) - 10(-5) M）使PTH依赖性cAMP产生降低了25 - 36%。我们的数据表明，近端小管细胞能够感知Ca++的生理相关变化，为调节1,25-二羟维生素D的产生或其他与液体和矿物质稳态相关的肾小管功能提供了一种潜在机制。