Department of Physiology, Pharmacology and Neuroscience, West Virginia University School of Medicine, Morgantown, WV, USA.
Department of Biochemistry, West Virginia University School of Medicine, Morgantown, WV, USA.
FASEB J. 2021 May;35(5):e21606. doi: 10.1096/fj.202100203R.
Na -K -2Cl cotransporter-1 (NKCC1) facilitates basolateral K and Cl uptake, supporting their efflux across mucosal membranes of colonic epithelial cells. NKCC1 activity has also been shown to be critical for electrogenic K secretion induced by aldosterone, which is known to stimulate large-conductance K (BK) channel expression in mucosal membranes. This study was aimed to (1) identify whether aldosterone enhances NKCC1 expression specifically to support BK-mediated K secretion and (2) to determine whether increased NKCC1 supports electrogenic Cl secretion in parallel to K secretion. Dietary Na depletion was used to induce secondary hyperaldosteronism in rats, or aldosterone was administered ex vivo to rat distal colonic mucosae. NKCC1-dependent electrogenic K or Cl secretion was measured as a function of short circuit current (I ). qRT-PCR, western blot, and immunofluorescence analyses were performed using standard techniques. Aldosterone enhanced NKCC1 and BKα expression and electrogenic K secretion in the distal colon, which was inhibited by either serosal bumetanide (NKCC1 inhibitor) or mucosal iberiotoxin (IbTX; BK channel blocker), but not TRAM-34 (IK channel blocker). Expression of NKCC1 and BKα proteins was enhanced in crypt cells of hyper-aldosterone rats. However, neither NKCC1-dependent Cl secretion nor CFTR (apical Cl channel) expression was enhanced by aldosterone. We conclude that aldosterone enhances NKCC1 to support BK-mediated K secretion independently of Cl secretion in the distal colon. The regulation of NKCC1 expression/K secretion by aldosterone may be a therapeutic target in treating gastrointestinal disorders associated with alterations in colonic K transport, such as colonic pseudo-obstruction, and hyperkalemia associated with renal disease.
钠钾 2 氯协同转运蛋白 1（NKCC1）促进基底外侧 K 和 Cl 的摄取，支持它们穿过结肠上皮细胞的黏膜膜的外流。NKCC1 活性也被证明对醛固酮诱导的电致性 K 分泌至关重要，醛固酮已知会刺激黏膜膜中大电导钾（BK）通道的表达。本研究旨在：（1）确定醛固酮是否专门增强 NKCC1 表达以支持 BK 介导的 K 分泌；（2）确定增加的 NKCC1 是否支持与 K 分泌平行的电致性 Cl 分泌。饮食性 Na 耗竭用于诱导大鼠继发性高醛固酮血症，或在体外用醛固酮处理大鼠远端结肠黏膜。作为短电路电流（I）的函数来测量 NKCC1 依赖性电致性 K 或 Cl 分泌。使用标准技术进行 qRT-PCR、western blot 和免疫荧光分析。醛固酮增强了远端结肠中的 NKCC1 和 BKα表达和电致性 K 分泌，这被腔侧布美他尼（NKCC1 抑制剂）或黏膜伊比替定（IbTX；BK 通道阻滞剂）抑制，但不被 TRAM-34（IK 通道阻滞剂）抑制。高醛固酮大鼠隐窝细胞中 NKCC1 和 BKα 蛋白的表达增强。然而，NKCC1 依赖性 Cl 分泌或 CFTR（顶端 Cl 通道）的表达均不受醛固酮增强。我们得出结论，醛固酮增强 NKCC1 以支持远端结肠中 BK 介导的 K 分泌，而不依赖于 Cl 分泌。醛固酮对 NKCC1 表达/K 分泌的调节可能是治疗与结肠 K 转运改变相关的胃肠道疾病的治疗靶点，例如结肠假性梗阻和与肾病相关的高钾血症。
