Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, Valdivia, Chile.
Universidad Austral de Chile, Valdivia, Chile.
J Physiol. 2018 Feb 1;596(3):393-407. doi: 10.1113/JP275178. Epub 2017 Dec 18.
K channels are important in intestinal epithelium as they ensure the ionic homeostasis and electrical potential of epithelial cells during anion and fluid secretion. Intestinal epithelium cAMP-activated anion secretion depends on the activity of the (also cAMP dependent) KCNQ1-KCNE3 K channel, but the secretory process survives after genetic inactivation of the K channel in the mouse. Here we use double mutant mice to investigate which alternative K channels come into action to compensate for the absence of KCNQ1-KCNE3 K channels. Our data establish that whilst Ca -activated K 3.1 channels are not involved, K two-pore domain TASK-2 K channels are major players providing an alternative conductance to sustain the intestinal secretory process. Work with double mutant mice lacking both TASK-2 and KCNQ1-KCNE3 channels nevertheless points to yet-unidentified K channels that contribute to the robustness of the cAMP-activated anion secretion process.
Anion and fluid secretion across the intestinal epithelium, a process altered in cystic fibrosis and secretory diarrhoea, is mediated by cAMP-activated CFTR Cl channels and requires the simultaneous activity of basolateral K channels to maintain cellular ionic homeostasis and membrane potential. This function is fulfilled by the cAMP-activated K channel formed by the association of pore-forming KCNQ1 with its obligatory KCNE3 β-subunit. Studies using mice show sizeable cAMP-activated intestinal anion secretion in the absence of either KCNQ1 or KCNE3 suggesting that an alternative K conductance must compensate for the loss of KCNQ1-KCNE3 activity. We used double mutant mouse and pharmacological approaches to identify such a conductance. Ca -dependent anion secretion can also be supported by Ca -dependent K 3.1 channels after independent CFTR activation, but cAMP-dependent anion secretion is not further decreased in the combined absence of K 3.1 and KCNQ1-KCNE3 K channel activity. We show that the K K channel TASK-2 is expressed in the epithelium of the small and large intestine. Tetrapentylammonium, a TASK-2 inhibitor, abolishes anion secretory current remaining in the absence of KCNQ1-KCNE3 activity. A double mutant mouse lacking both KCNQ1-KCNE3 and TASK-2 showed a much reduced cAMP-mediated anion secretion compared to that observed in the single KCNQ1-KCNE3 deficient mouse. We conclude that KCNQ1-KCNE3 and TASK-2 play major roles in the intestinal anion and fluid secretory phenotype. The persistence of an, admittedly reduced, secretory activity in the absence of these two conductances suggests that further additional K channel(s) as yet unidentified contribute to the robustness of the intestinal anion secretory process.
肠道上皮细胞中的 K 通道很重要，因为它们确保了上皮细胞在阴离子和液体分泌过程中的离子稳态和膜电位。肠道上皮细胞 cAMP 激活的阴离子分泌依赖于（也依赖于 cAMP）KCNQ1-KCNE3 K 通道的活性，但在小鼠中 K 通道的基因失活后，分泌过程仍然存活。在这里，我们使用双突变小鼠来研究哪种替代 K 通道会起作用以弥补 KCNQ1-KCNE3 K 通道的缺失。我们的数据表明，虽然钙激活的 K 3.1 通道不参与，但双孔域 TASK-2 K 通道是主要的参与者，提供了一种替代电导来维持肠道分泌过程。然而，对缺乏 TASK-2 和 KCNQ1-KCNE3 两种通道的双突变小鼠的研究表明，仍有尚未确定的 K 通道有助于 cAMP 激活的阴离子分泌过程的稳健性。
跨肠道上皮细胞的阴离子和液体分泌是囊性纤维化和分泌性腹泻改变的过程，由 cAMP 激活的 CFTR Cl 通道介导，需要同时激活基底外侧 K 通道以维持细胞离子稳态和膜电位。这种功能由与 obligatory KCNE3 β 亚基相关联的孔形成 KCNQ1 形成的 cAMP 激活的 K 通道来完成。使用小鼠的研究表明，即使没有 KCNQ1 或 KCNE3，也存在相当大的 cAMP 激活的肠道阴离子分泌，这表明必须有替代的 K 电导来弥补 KCNQ1-KCNE3 活性的丧失。我们使用双突变小鼠和药理学方法来鉴定这种电导。在独立激活 CFTR 后，Ca 依赖性阴离子分泌也可以由 Ca 依赖性 K 3.1 通道支持，但在 K 3.1 和 KCNQ1-KCNE3 K 通道活性同时缺失的情况下，cAMP 依赖性阴离子分泌不会进一步降低。我们表明，K K 通道 TASK-2 在小肠和大肠的上皮细胞中表达。四戊基铵，一种 TASK-2 抑制剂，消除了在缺乏 KCNQ1-KCNE3 活性的情况下仍然存在的阴离子分泌电流。与在单一 KCNQ1-KCNE3 缺乏的小鼠中观察到的相比，缺乏 KCNQ1-KCNE3 和 TASK-2 的双突变小鼠显示出的 cAMP 介导的阴离子分泌明显减少。我们得出的结论是，KCNQ1-KCNE3 和 TASK-2 在肠道阴离子和液体分泌表型中起主要作用。在缺乏这两种电导的情况下，确实减少的分泌活性仍然存在，这表明尚未确定的其他 K 通道有助于肠道阴离子分泌过程的稳健性。
