Quantification of K+ secretion through apical low-conductance K channels in the CCD
Quantification of K+ secretion through apical low-conductance K channels in the CCD
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DOI：
10.1152/ajprenal.00471.2004
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发表时间：
2005-07-01
影响因子：
4.2
通讯作者：
Palmer, LG
中科院分区：
文献类型：
--
作者：
Gray, DA;Frindt, G;Palmer, LG
通过CCD中顶端低电导K通道的K+分泌的定量。美国肾脏生理学杂志289：F117 - F126，2005年。首次发表于2005年2月22日; doi：10.1152/ajprenal。00471.2004. - 在大鼠皮质集合管（CCD）主细胞顶膜细胞贴附贴片上，测定了单个小电导K+（SK）通道的外向和内向电流。电流表现为轻度内向整流，移液管中[K+]较高（K-p（+）），随着K-p（+）降低，[K +]降低。内向电导与K-p（+）呈双曲线关系，半最大电导接近20 mM。在反转电位附近测量的外向电导也随K-p（+）从15 pS（K-p（+）= 0）增加到50 pS（K-p（+）接近134 mM）。SK通道密度测量为细胞附着贴片中每个贴片的传导通道数。如前所述，当动物高钾饮食7天时，通道密度增加。在密封前至少5分钟向浴中加入8-cpt-cAMP可更大程度地增加SK通道密度，尽管这种增加与高钾饮食的作用不加和。相比之下，增加钠通道活性，评估为全细胞阿米洛利敏感电流，由于钾负荷和8-cpt-cAMP治疗是加性的。单通道电导和通道密度被用作CCD的简单数学模型的输入，以预测跨上皮Na+和K+转运速率作为顶端Na+渗透性和K+电导、基底侧泵速率和K+电导以及细胞旁电导的函数。与这些参数的测量值，模型预测的传输速率与孤立的，灌注小管中测量值的一致性很好。SK通道的数量和属性占K+运输的CCD在所有的生理条件下测试。
Quantification of K+ secretion through apical low-conductance K channels in the CCD. Am J Physiol Renal Physiol 289: F117 - F126, 2005. First published February 22, 2005; doi: 10.1152/ajprenal. 00471.2004. - Outward and inward currents through single small-conductance K+ (SK) channels were measured in cell-attached patches of the apical membrane of principal cells of the rat cortical collecting duct ( CCD). Currents showed mild inward rectification with high [K+] in the pipette (K-p(+)), which decreased as K-p(+) was lowered. Inward conductances had a hyperbolic dependence on K-p(+) with half-maximal conductance at similar to 20 mM. Outward conductances, measured near the reversal potential, also increased with K-p(+) from 15 pS (K-p(+) = 0) to 50 pS (K-p(+) similar to 134 mM). SK channel density was measured as the number of conducting channels per patch in cell-attached patches. As reported previously, channel density increased when animals were on a high-K diet for 7 days. Addition of 8-cpt-cAMP to the bath at least 5 min before making a seal increased SK channel density to an even greater extent, although this increase was not additive with the effect of a high-K diet. In contrast, increases in Na channel activity, assessed as the whole cell amiloride-sensitive current, due to K loading and 8-cpt-cAMP treatment were additive. Single-channel conductances and channel densities were used as inputs to a simple mathematical model of the CCD to predict rates of transepithelial Na+ and K+ transport as a function of apical Na+ permeability and K+ conductance, basolateral pump rates and K+ conductance, and the paracellular conductance. With measured values for these parameters, the model predicted transport rates that were in good agreement with values measured in isolated, perfused tubules. The number and properties of SK channels account for K+ transport by the CCD under all physiological conditions tested.