Department of Pediatrics/Gastroenterology and Hepatology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Am J Physiol Gastrointest Liver Physiol. 2011 Jan;300(1):G82-98. doi: 10.1152/ajpgi.00245.2010. Epub 2010 Oct 28.
We examined the cell-specific subcellular expression patterns for sodium- and potassium-coupled chloride (NaK2Cl) cotransporter 1 (NKCC1), Na(+) bicarbonate cotransporter (NBCe1), cystic fibrosis transmembrane conductance regulator (CFTR), and Na(+)/H(+) exchanger 3 (NHE3) to understand the functional plasticity and synchronization of ion transport functions along the crypt-villus axis and its relevance to intestinal disease. In the unstimulated intestine, all small intestinal villus enterocytes coexpressed apical CFTR and NHE3, basolateral NBCe1, and mostly intracellular NKCC1. All (crypt and villus) goblet cells strongly expressed basolateral NKCC1 (at approximately three-fold higher levels than villus enterocytes), but no CFTR, NBCe1, or NHE3. Lower crypt cells coexpressed apical CFTR and basolateral NKCC1, but no NHE3 or NBCe1 (except NBCe1-expressing proximal colonic crypts). CFTR, NBCe1, and NKCC1 colocalized with markers of early and recycling endosomes, implicating endocytic recycling in cell-specific anion transport. Brunner's glands of the proximal duodenum coexpressed high levels of apical/subapical CFTR and basolateral NKCC1, but very low levels of NBCe1, consistent with secretion of Cl(-)-enriched fluid into the crypt. The cholinergic agonist carbachol rapidly (within 10 min) reduced cell volume along the entire crypt/villus axis and promoted NHE3 internalization into early endosomes. In contrast, carbachol induced membrane recruitment of NKCC1 and CFTR in all crypt and villus enterocytes, NKCC1 in all goblet cells, and NBCe1 in all villus enterocytes. These observations support regulated vesicle traffic in Cl(-) secretion by goblet cells and Cl(-) and HCO(3)(-) secretion by villus enterocytes during the transient phase of cholinergic stimulation. Overall, the carbachol-induced membrane trafficking profile of the four ion transporters supports functional plasticity of the small intestinal villus epithelium that enables it to conduct both absorptive and secretory functions.
我们研究了钠-钾-2 氯共转运蛋白 1（NKCC1）、钠-碳酸氢盐共转运蛋白（NBCe1）、囊性纤维化跨膜电导调节因子（CFTR）和钠/氢交换器 3（NHE3）在细胞特异性亚细胞表达模式，以了解离子转运功能在隐窝-绒毛轴上的功能可塑性和同步性及其与肠道疾病的相关性。在未受刺激的肠道中，所有小肠绒毛状肠细胞均共表达顶端 CFTR 和 NHE3、基底外侧 NBCe1 和大部分细胞内 NKCC1。所有（隐窝和绒毛）杯状细胞强烈表达基底外侧 NKCC1（比绒毛状肠细胞高约三倍），但不表达 CFTR、NBCe1 或 NHE3。较低的隐窝细胞共表达顶端 CFTR 和基底外侧 NKCC1，但不表达 NHE3 或 NBCe1（除了表达 NBCe1 的近端结肠隐窝）。CFTR、NBCe1 和 NKCC1 与早期和再循环内体的标志物共定位，提示内体再循环在细胞特异性阴离子转运中起作用。近端十二指肠的 Brunner 腺共表达高水平的顶端/亚顶端 CFTR 和基底外侧 NKCC1，但 NBCe1 水平非常低，这与富含 Cl(-)的液体分泌到隐窝中一致。胆碱能激动剂 carbachol 可快速（在 10 分钟内）沿整个隐窝-绒毛轴缩小细胞体积，并促进 NHE3 内吞进入早期内体。相比之下，carbachol 在所有隐窝和绒毛状肠细胞中诱导 NKCC1 和 CFTR 的膜募集，在所有杯状细胞中诱导 NKCC1 的膜募集，在所有绒毛状肠细胞中诱导 NBCe1 的膜募集。这些观察结果支持在胆碱能刺激的短暂阶段，杯状细胞中 Cl(-)分泌的受调控的囊泡运输以及绒毛状肠细胞中 Cl(-)和 HCO3(-)分泌的受调控的囊泡运输。总的来说，四种离子转运体的 carbachol 诱导的膜转运谱支持小肠绒毛上皮的功能可塑性，使其能够进行吸收和分泌功能。
