Mechanisms for K secretion and K reabsorption in the distal tubule

以往的研究表明，肾小管周围K^的急性升高可促进兔肾脏灌流皮质集合管(CCD)的K^分泌和Na^重吸收。为探讨其细胞机制，我们采用微电极技术，通过迅速将浴液从2.5 mm K~(-1)增加到8.5 mm K~(-1)，观察了对照组和脱氧皮质酮醋酸酯(DOCA)处理组兔离体主集合管细胞在基础侧Na、K泵急性刺激后的膜特性。这在两组肾小管中引起，第一，短暂的超极化，第二，跨上皮膜电压、基底膜电压和顶膜电压的持续去极化。超极化初期跨膜电导(G_T)和膜阻力分数(Fr_A)不变，去极化时G_T升高，Fr_A降低。用含有阿米洛利或Ba2&gt；的溶液灌流管腔可减弱高K^引起的心尖电信号改变，而底侧毛花蛇舌草素则可使K^升高时的尖电反应和基侧电反应消失。根据这些结果，我们得出结论：1)急性升高基线K^，激活了基线Na^，K^泵，继而使心尖Na^和K^电导升高；2)DOCA预处理增加了基线K^电导，并增强了对基线K^、K泵活性和心尖阳离子电导升高的响应。

Previous studies that an acute elevation of peritubular K^+ enhances K^+ secretion and Na^+ reabsorption in the isolated perfused cortical collecting duct (CCD) from rabbit kidneys. To determine the undelying cellular mechanisms, we used microelectrode techniques to assess the membrane properties of principal collecting duct cells in isolated perfused CCDs of control and desoxycorticosterone acetate (DOCA) -treated rabbits following acute stimulation of the basolateral Na^+, K^+ pump by rapidly increasing the bath solution form 2.5 to 8.5 mM K^+. This induced in both groups of tubules, first, a short-lasting hyperpolarization and second, a sustained phase of depolarization of transepithelial, basolateral, and apical membrane voltages. Whereas the transepithelial conductance (G_T) and fractional apical membrane resistance (fR_A) remained unchanged during the initial phase of hyperpolarization, G_T increased during depolarization and fR_A decreased. Perfusion of the lumen with solutions containing either amiloride or Ba^<2+> attenuated the high K^+-induced apical electrical changes, and basolateral strophanthidin abolished both apical and basolateral electrical responses during elevation of K^+ in the bath. From these results we conclude : 1) Acute elevation of basolateral K^+ activates the basolateral Na^+, K^+ pump, which secondarily elevates the apical Na^+ and K^+ conductances ; 2) DOCA pretreatment increases the basolateral K^+ conductances and augments the response to the rise of K^+ of both basolateral Na^+, K^+ pump activity and apical cation conductances.