Pat-1（Slc26a6）Cl(-)/HCO₃(-)交换在小鼠十二指肠降部隐窝上皮中的功能活性。
Functional activity of Pat-1 (Slc26a6) Cl(−)/HCO₃(−) exchange in the lower villus epithelium of murine duodenum.
机构信息
Dalton Cardiovascular Research Center, University of Missouri, Columbia, 65211, USA.
出版信息
Acta Physiol (Oxf). 2011 Jan;201(1):21-31. doi: 10.1111/j.1748-1716.2010.02210.x. Epub 2010 Nov 12.
AIMS
The apical membrane anion exchanger putative anion transporter-1 (Pat-1) is expressed at significant levels in the lower villus epithelium of murine duodenum. However, previous studies of Cl(−)/HCO₃(−) exchange in the lower villus have failed to demonstrate Pat-1 function. Those studies routinely included luminal glucose which induces Na(+) -coupled glucose transport and acidifies the villus epithelium. Since Pat-1 has been proposed to be an electrogenic 1Cl(−)/2HCO₃(−) exchanger, membrane depolarization or cell acidification during glucose transport may obscure Pat-1 activity. Therefore, we investigated the effects of luminal glucose on Cl(−)(IN)/HCO₃(−) (OUT) exchange activity in the lower villus epithelium.
METHODS
Cl(−)(IN) /HCO (−) (OUT) exchange of villus epithelium in duodenal mucosa from Pat-1 knockout (KO), Slc26a3 [down-regulated in adenoma (Dra)] KO, cystic fibrosis transmembrane conductance regulator (Cftr) KO and wild-type (WT) littermate mice was measured using the pH-sensitive dye 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein. Short-circuit current (I(sc) ) was measured in Ussing chambers.
RESULTS
During glucose absorption, Cl(−)(IN)/HCO₃(−) (OUT) exchange in the lower villus epithelium was abolished in the Dra KO and unaffected in the Pat-1 KO relative to WT. However, during electroneutral mannose absorption or electrogenic α-D-methyl glucoside absorption, Cl(−)(IN) /HCO₃(−) (OUT) exchange was reduced in both Pat-1 KO and Dra KO villi. Exposure to high [K(+)] abolished Cl(−)(IN) /HCO₃(−) (OUT) exchange in the Dra KO but not the Dra/Cftr double KO epithelium, suggesting that Pat-1 activity is little affected by membrane depolarization except in the presence of Cftr.
CONCLUSIONS
The metabolic and electrogenic activity of glucose transport obscures Cl(−)(IN) /HCO₃(−) (OUT) exchange activity of Pat-1 in the lower villus. The inhibitory effects of membrane depolarization on Pat-1 Cl(−)(IN) /HCO₃(−) (OUT) exchange may require concurrent membrane association with Cftr.
目的
顶膜阴离子交换体假定阴离子转运蛋白-1（Pat-1）在鼠十二指肠的下部绒毛上皮中表达水平较高。然而，先前关于下部绒毛中 Cl(-)/HCO₃(-)交换的研究未能证明 Pat-1 功能。这些研究通常包括腔腔内葡萄糖，葡萄糖可诱导 Na(+) -偶联葡萄糖转运并使绒毛上皮酸化。由于 Pat-1 被提议为一种电致 1Cl(-)/2HCO₃(-)交换体，因此葡萄糖转运过程中的膜去极化或细胞酸化可能会掩盖 Pat-1 活性。因此，我们研究了腔腔内葡萄糖对下部绒毛上皮中 Cl(-)(IN)/HCO₃(-) (OUT)交换活性的影响。
方法
使用 pH 敏感染料 2',7'-双-(2-羧乙基)-5-(和-6)-羧基荧光素测量来自 Pat-1 敲除（KO）、Slc26a3[下调腺瘤（Dra）]KO、囊性纤维化跨膜电导调节剂（Cftr）KO 和野生型（WT）同窝小鼠十二指肠黏膜绒毛上皮的 Cl(-)(IN)/HCO₃(-) (OUT)交换。在 Ussing 室中测量短路电流（I(sc)）。
结果
在葡萄糖吸收过程中，与 WT 相比，Dra KO 中下部绒毛上皮的 Cl(-)(IN)/HCO₃(-) (OUT)交换被完全阻断，而 Pat-1 KO 中则不受影响。然而，在电中性甘露糖吸收或电致性α-D-甲基葡萄糖吸收过程中，Pat-1 KO 和 Dra KO 绒毛中的 Cl(-)(IN) /HCO₃(-) (OUT)交换均减少。暴露于高[K(+)]会消除 Dra KO 中的 Cl(-)(IN)/HCO₃(-) (OUT)交换，但不会消除 Dra/Cftr 双 KO 上皮中的 Cl(-)(IN)/HCO₃(-) (OUT)交换，这表明除了 Cftr 之外，膜去极化对 Pat-1 活性的影响很小。
结论
葡萄糖转运的代谢和电致活性掩盖了下部绒毛中 Pat-1 的 Cl(-)(IN)/HCO₃(-) (OUT)交换活性。膜去极化对 Pat-1 Cl(-)(IN)/HCO₃(-) (OUT)交换的抑制作用可能需要与 Cftr 同时膜结合。
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