Institute of Physiology, University of Regensburg , Regensburg , Germany.
Department of Pathology, Brigham and Women's Hospital , Boston, Massachusetts.
Am J Physiol Renal Physiol. 2018 Oct 1;315(4):F834-F843. doi: 10.1152/ajprenal.00554.2017. Epub 2017 Dec 27.
The secretion of the protease renin from renal juxtaglomerular cells is enhanced by subnormal extracellular calcium concentrations. The mechanisms underlying this atypical effect of calcium have not yet been unraveled. We therefore aimed to characterize the effect of extracellular calcium concentration on calcium handling of juxtaglomerular cells and on renin secretion in more detail. For this purpose, we used a combination of experiments with isolated perfused mouse kidneys and direct calcium measurements in renin-secreting cells in situ. We found that lowering of the extracellular calcium concentration led to a sustained elevation of renin secretion. Electron-microscopical analysis of renin-secreting cells exposed to subnormal extracellular calcium concentrations revealed big omega-shaped structures resulting from the intracellular fusion and subsequent emptying of renin storage vesicles. The calcium concentration dependencies as well as the kinetics of changes were rather similar for renin secretion and for renovascular resistance. Since vascular resistance is fundamentally influenced by myosin light chain kinase (MLCK), myosin light chain phosphatase (MLCP), and Rho-associated protein kinase (Rho-K) activities, we examined the effects of MLCK-, MLCP-, and Rho-K inhibitors on renin secretion. Only MLCK inhibition stimulated renin secretion. Conversely, inhibition of MCLP activity lowered perfusate flow and strongly inhibited renin secretion, which could not be reversed by lowering of the extracellular calcium concentration. Renin-secreting cells and smooth muscle cells of afferent arterioles showed immunoreactivity of MLCK. These findings suggest that the inhibitory effect of calcium on renin secretion could be explained by phosphorylation-dependent processes under control of the MLCK.
肾球旁细胞分泌的蛋白酶肾素受细胞外钙浓度异常升高的促进。钙对这种非典型作用的机制尚未阐明。因此，我们旨在更详细地研究细胞外钙浓度对球旁细胞钙处理和肾素分泌的影响。为此，我们结合使用了分离灌注的小鼠肾脏实验和原位分泌肾素细胞的直接钙测量。我们发现，降低细胞外钙浓度会导致肾素分泌持续升高。暴露于异常低的细胞外钙浓度的分泌肾素的细胞的电子显微镜分析显示，由于细胞内融合和随后的肾素储存小泡排空而产生的大的ω形结构。肾素分泌和肾血管阻力的钙浓度依赖性以及变化动力学非常相似。由于血管阻力主要受肌球蛋白轻链激酶 (MLCK)、肌球蛋白轻链磷酸酶 (MLCP) 和 Rho 相关蛋白激酶 (Rho-K) 活性的影响，我们检查了 MLCK、MLCP 和 Rho-K 抑制剂对肾素分泌的影响。只有 MLCK 抑制刺激肾素分泌。相反，抑制 MLCP 活性降低灌流液流量并强烈抑制肾素分泌，这不能通过降低细胞外钙浓度来逆转。肾素分泌细胞和入球小动脉的平滑肌细胞显示出 MLCK 的免疫反应性。这些发现表明，钙对肾素分泌的抑制作用可以通过 MLCK 控制的磷酸化依赖性过程来解释。
