Leeds Institute of Molecular Medicine, Saint James's University Hospital, Leeds, United Kingdom.
Am J Physiol Cell Physiol. 2012 Aug 1;303(3):C328-33. doi: 10.1152/ajpcell.00099.2012. Epub 2012 May 30.
cAMP induces both active Cl(-) and active K(+) secretion in mammalian colon. It is generally assumed that a mechanism for K(+) exit is essential to maintain cells in the hyperpolarized state, thus favoring a sustained Cl(-) secretion. Both Kcnn4c and Kcnma1 channels are located in colon, and this study addressed the questions of whether Kcnn4c and/or Kcnma1 channels mediate cAMP-induced K(+) secretion and whether cAMP-induced K(+) secretion provides the driving force for Cl(-) secretion. Forskolin (FSK)-enhanced short-circuit current (indicator of net electrogenic ion transport) and K(+) fluxes were measured simultaneously in colonic mucosa under voltage-clamp conditions. Mucosal Na(+) orthovanadate (P-type ATPase inhibitor) inhibited active K(+) absorption normally present in rat distal colon. In the presence of mucosal Na(+) orthovanadate, serosal FSK induced both K(+) and Cl(-) secretion. FSK-induced K(+) secretion was 1) not inhibited by either mucosal or serosal 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34; a Kcnn4 channel blocker), 2) inhibited (92%) by mucosal iberiotoxin (Kcnma1 channel blocker), and 3) not affected by mucosal cystic fibrosis transmembrane conductance regulator inhibitor (CFTR(inh)-172). By contrast, FSK-induced Cl(-) secretion was 1) completely inhibited by serosal TRAM-34, 2) not inhibited by either mucosal or serosal iberiotoxin, and 3) completely inhibited by mucosal CFTR(inh)-172. These results indicate that cAMP-induced colonic K(+) secretion is mediated via Kcnma1 channels located in the apical membrane and most likely contributes to stool K(+) losses in secretory diarrhea. On the other hand, cAMP-induced colonic Cl(-) secretion requires the activity of Kcnn4b channels located in the basolateral membrane and is not dependent on the concurrent activation of apical Kcnma1 channels.
cAMP 可诱导哺乳动物结肠中的活性 Cl(-)和活性 K(+)分泌。人们普遍认为，K(+)外排的机制对于维持细胞的超极化状态至关重要，从而有利于持续的 Cl(-)分泌。Kcnn4c 和 Kcnma1 通道都位于结肠中，本研究旨在探讨 Kcnn4c 和/或 Kcnma1 通道是否介导 cAMP 诱导的 K(+)分泌，以及 cAMP 诱导的 K(+)分泌是否为 Cl(-)分泌提供驱动力。在电压钳条件下，同时测量福司可林（FSK）增强的短路电流（指示净电致离子转运）和结肠黏膜中的 K(+)通量。黏膜 Na(+) orthovanadate（P 型 ATP 酶抑制剂）抑制了大鼠远端结肠中存在的活性 K(+)吸收。在存在黏膜 Na(+) orthovanadate 的情况下，血清 FSK 可诱导 K(+)和 Cl(-)分泌。FSK 诱导的 K(+)分泌 1）不受黏膜或血清 1-[(2-氯苯基)二苯甲基]-1H-吡唑（TRAM-34；Kcnn4 通道阻断剂）的抑制，2）被黏膜 iberiotoxin（Kcnma1 通道阻断剂）抑制（92%），3）不受黏膜囊性纤维化跨膜电导调节剂抑制剂（CFTR(inh)-172）的影响。相比之下，FSK 诱导的 Cl(-)分泌 1）完全被血清 TRAM-34 抑制，2）不受黏膜或血清 iberiotoxin 的抑制，3）完全被黏膜 CFTR(inh)-172 抑制。这些结果表明，cAMP 诱导的结肠 K(+)分泌是通过位于顶膜的 Kcnma1 通道介导的，并且很可能导致分泌性腹泻中的粪便 K(+)丢失。另一方面，cAMP 诱导的结肠 Cl(-)分泌需要位于基底外侧膜的 Kcnn4b 通道的活性，并且不依赖于同时激活顶端的 Kcnma1 通道。
