细胞外钠的生理变化直接控制人类近端肾小管的生长和转运。

Physiological changes in extracellular sodium directly control human proximal tubule growth and transport.

作者信息

Johnson D W, Saunders H J, Poronnik P, Cook D I, Field M J, Pollock C A

机构信息

Department of Medicine, University of Sydney, Sydney, Australia 2006.

出版信息

Pflugers Arch. 1998 Jan;435(2):211-8. doi: 10.1007/s004240050503.

DOI:10.1007/s004240050503

PMID:9382933

Abstract

In order to examine the nature and potential mechanisms of action of extracellular sodium on human proximal tubule growth and transport, quiescent primary cultures of human proximal tubule cells (PTC) were incubated for 24 h in serum-free, growth-factor-free culture media containing low (130 mmol/l), control (140 mmol/l) or high (150 mmol/l) Na+. Compared to control conditions, cells exposed to a high Na+ concentration demonstrated stimulated thymidine incorporation (121.8 +/- 7.6%, P < 0.05) and increased cellular protein content (139.7 +/- 9.9%, P < 0.05); the latter arising from suppressed protein degradation ([3H]valine release 72.3 +/- 2.5%, P < 0.01) and unchanged protein synthesis ([3H]valine incorporation 98.5 +/- 2.6%, P > 0.1). Substitution of choline chloride for NaCl did not replicate these effects. Conversely, cells incubated in low-Na+ media showed reduced thymidine incorporation (77.2 +/- 4.4%, P < 0. 05), reduced protein synthesis (60.6 +/- 4.3%, P < 0.01), reduced protein degradation (79.5 +/- 1.8%, P < 0.01) and an unaltered protein content (102.4 +/- 8.8%). A role for apical Na+/H+ exchange (NHE) activity in mediating Na+-dependent alterations in PTC growth was suggested by the findings of increased apical, ethylisopropylamiloride- (EIPA)-sensitive 22Na+ uptake in the presence of a high Na+ concentration (159 +/- 19% of control, P < 0. 05) and concentration-dependent inhibition of cellular growth by EIPA at levels corresponding to those producing inhibition of apical NHE. Conditioned media from low Na+, control or high Na+ PTC contained comparable amounts of platelet-derived growth factor-AB (1. 19 +/- 0.23, 1.14 +/- 0.22 and 1.28 +/- 0.20 ng/mg protein, P > 0.1) and transforming growth factor-beta1 (1.76 +/- 0.32, 1.73 +/- 0.33 and 1.45 +/- 0.28 ng/mg protein, P > 0.1), and did not exhibit autocrine growth factor activity on separate PTC following adjustment of Na+ concentrations to 140 mmol/l by dialysis. Similarly, low-Na+, control or high-Na+ media did not modify the mitogenic responsiveness of PTC to insulin-like growth factor-I (IGF-I) or alter the affinity or number of PTC IGF-I binding sites. The results confirm that physiological increases in extracellular Na+ concentration directly stimulate human proximal tubule growth and Na+ transport. Such stimulation does not appear to be mediated by altered PTC secretion of, or responsiveness to, cytokines known to affect tubule growth and transport.

摘要

为了研究细胞外钠对人近端肾小管生长和转运的作用性质及潜在机制，将人近端肾小管细胞（PTC）的静态原代培养物在含低（130 mmol/L）、对照（140 mmol/L）或高（150 mmol/L）Na⁺的无血清、无生长因子的培养基中孵育24小时。与对照条件相比，暴露于高Na⁺浓度的细胞表现出胸苷掺入增加（121.8±7.6%，P<0.05）和细胞蛋白含量增加（139.7±9.9%，P<0.05）；后者源于蛋白质降解受抑制（[³H]缬氨酸释放72.3±2.5%，P<0.01）且蛋白质合成未改变（[³H]缬氨酸掺入98.5±2.6%，P>0.1）。用氯化胆碱替代NaCl不能重现这些效应。相反，在低Na⁺培养基中孵育的细胞胸苷掺入减少（77.2±4.4%，P<0.05），蛋白质合成减少（60.6±4.3%，P<0.01），蛋白质降解减少（79.5±1.8%，P<0.01）且蛋白含量未改变（102.4±8.8%）。在高Na⁺浓度（159±19%对照，P<0.05）下顶端乙基异丙基氨氯地平（EIPA）敏感的²²Na⁺摄取增加，以及EIPA在产生顶端NHE抑制的相应水平对细胞生长的浓度依赖性抑制，提示顶端Na⁺/H⁺交换（NHE）活性在介导PTC生长中Na⁺依赖性改变方面起作用。来自低Na⁺、对照或高Na⁺ PTC的条件培养基含有相当数量的血小板衍生生长因子-AB（1.19±0.23、1.14±0.22和1.28±0.20 ng/mg蛋白，P>0.1）和转化生长因子-β1（1.76±0.32、1.73±0.33和1.45±0.28 ng/mg蛋白，P>0.1），并且在通过透析将Na⁺浓度调整至140 mmol/L后，对单独的PTC未表现出自分泌生长因子活性。同样，低Na⁺、对照或高Na⁺培养基未改变PTC对胰岛素样生长因子-I（IGF-I）的促有丝分裂反应性，也未改变PTC IGF-I结合位点的亲和力或数量。结果证实细胞外Na⁺浓度的生理性升高直接刺激人近端肾小管生长和Na⁺转运。这种刺激似乎不是由已知影响肾小管生长和转运的细胞因子的PTC分泌改变或反应性改变介导的。