MATURATION OF CATION TRANSPORT IN DISTAL NEPHRON

远端肾单位中阳离子传输的成熟

• 批准号: 2140544
• 负责人: Lisa M. Satlin
• 金额: $ 29.19万
• 依托单位: ALBERT EINSTEIN COLLEGE OF MEDICINE
• 依托单位国家: 美国
• 财政年份: 1986
• 资助国家: 美国
• 起止时间: 1986-08-01 至 1998-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2140544
• 关键词: apical membrane; growth /development; infant animal; laboratory rabbit; potassium; potassium channel; renal tubular transport; sodium; sodium potassium exchanging ATPase; voltage /patch clamp

Growing subjects are in a state of positive K balance and have a limited ability to excrete K. This suggests that the immature kidney has a limited capacity for K secretion and/or enhanced ability to reabsorb K. The major regulatory site of K secretion in the kidney is the cortical collecting duct (CCD). In contrast to the high rates of net K secretion observed in CCDs isolated from adult animals and microperfused in vitro, segments from neonatal animals show no significant K transport. Yet, these same neonatal segments absorb Na at a rate half that measured in the adult, suggesting there exists a fundamental difference in cation transport mechanisms between the neonate and adult. K secretion in the CCD, mediated by principal cells, is determined by a two step process: active K uptake into the cell by Na-K-ATPase and passive diffusion down a favorable electrochemical gradient through apical K channels. To determine whether a paucity of apical K secretory channels limits net K secretion early in life, we will use patch clamp analysis to compare the apical K conductances of neonatal and mature principal cells. To examine whether the absence of conducting K secretory channels is due to a low open probability (P-O) of existing channels and/or a low channel number (N), we will next determine whether exposure of the neonatal CCD to factors known to increase P-O or N induces net K secretion. The discrepancy between onset of Na and K transport in the neonatal CCD suggests that qualitative changes in the transepithelial Na absorptive pathway occur during postnatal differentiation. To test this, we will compare the apical Na conductances (patch clamp analysis), membrane transporters active in Na reabsorption (helium glow photometry), and Na-K-ATPase activity (ouabain- sensitive basolateral 86Rb uptake) in neonatal and mature principal cells; the latter findings will be correlated with measurements of basolateral membrane surface area (electron microscopy). Because clearance studies in the neonate indicate significant K retention, we will also test the hypothesis that enhanced K absorption in the neonate reduces net urinary K excretion. To assess the K absorptive capacity of the CCD and outer medullary collecting duct (OMCD), we will determine the contribution of K absorption, measured as unidirectional lumen-to-bath 86Rb fluxes, to net K transport in segments isolated from maturing animals. Should we document significant K absorption early in life, we will test whether K absorption is coupled to H secretion by H-K-ATPase, a transporter immunocytochemically identified in intercalated cells. That population of intercalated cells possessing functional H-K-ATPase will then be identified and the polarity and activity of H-K exchange measured to determine if there is a maturational change in activity of this pump. The studies proposed in this application should help us to understand the physiologic basis for the limited K secretory capacity of the neonatal CCD and provide broad insight into the regulation of the K secretory process and its interrelationship with the mechanism of Na absorption.

成长的受试者处于积极的k平衡状态，并且有限 排泄K的能力。这表明未成熟的肾脏有限 K分泌的能力和/或增强重新吸收K的能力。 肾脏中K分泌的调节部位是皮质收集 管道（CCD）。与在 从成年动物和体外微养殖的CCD，来自 新生动物没有明显的K运输。但是，这些新生儿 段以成年人测量的一半吸收Na，表明 阳离子运输机制存在根本差异 在新生儿和成人之间。 CCD中的K分泌，由 主细胞由两个步骤确定：主动k吸收进入 NA-K-ATPase和被动扩散的细胞降低 通过顶端K通道的电化学梯度。确定是否 根尖k分泌渠道的稀少限制了净k分泌 生活，我们将使用斑块夹分析比较顶端K 新生儿和成熟的主要细胞的电导。检查是否 缺乏进行K分泌通道是由于开放率低 现有信道和/或低通道号（n）的概率（P-O），我们 接下来，将确定新生儿CCD是否暴露于已知因素 增加p-o或n诱导净k分泌。之间的差异 新生儿CCD中Na和K运输的发作表明定性 跨度Na吸收途径的变化发生在 产后分化。为了测试这一点，我们将比较顶端NA 电导（贴片夹分析），活性Na的膜转运蛋白 重吸收（氦发光光度法）和Na-k-ATPase活性（ouabain- 新生儿和成熟的主要细胞中敏感的基底外侧86RB摄取）； 后一个发现将与基底外侧的测量相关 膜表面积（电子显微镜）。因为清除研究 新生儿表示明显的k保留率，我们还将测试 假设增强了新生儿的K吸收可减少净尿液 k排泄物。评估CCD和外部的K吸收能力 髓质收集管（OMCD），我们将确定K的贡献 吸收，以单向管道到浴86rb的通量测量到净 k从成熟动物分离的细分市场中的运输。我们应该记录 生命早期的大量K吸收，我们将测试K吸收是否 由转运蛋白H-K-ATPase耦合到H分泌 免疫细胞化学在插入的细胞中鉴定出来。那个人口 然后，具有功能性H-K-ATPase的插入细胞将是 确定的以及H-K交换的极性和活性 确定该泵的活动是否成熟。这 本应用程序提出的研究应帮助我们了解 新生儿CCD的有限K分泌能力的生理基础 并为K分泌过程的调节提供广泛的见解 它与NA吸收机制的相互关系。