白蛋白向大鼠肠腔的转运。

Transport of albumin into the intestinal lumen of the rat.

作者信息

Kimm M H, Hardin J A, Gall D G

机构信息

Gastrointestinal Research Group, University of Calgary, AB, Canada.

出版信息

Can J Physiol Pharmacol. 1997 Mar;75(3):193-8.

PMID:9164701

Abstract

The intestine is considered a major site for the breakdown and clearance of serum proteins. The mechanism of transport of macromolecules from the serosa into the lumen is unclear. The present study was designed to characterize the serosal to mucosal movement of albumin. Transport of bovine serum albumin (BSA) was assessed in short-circuited Ussing chambers, using stripped rat jejunum devoid of Peyer's patches. To define the kinetics of serosal to mucosal albumin transport the serosal surface was exposed to BSA at varying concentrations (0.5-5 mg.mL-1). Fluids from the mucosal compartment were sampled over time and assayed for immunologically intact BSA by ELISA. All subsequent experiments utilized a concentration of cold BSA (2 mg.mL-1) that produced maximal levels of intact BSA transport. To assess total BSA transport (intact BSA plus degraded BSA), 10 microCi (1 Ci = 37 GBq) 125I-labelled BSA was added to the serosal surface in addition to 2 mg.mL-1 cold BSA. To further characterize BSA transport tissues were treated with sodium fluoride (NaF) (metabolic inhibitor) or colchicine (an inhibitor of microtubule polymerization) or with the nerve blocker tetrodotoxin (TTX). All experiments using inhibitors were performed in paired tissues obtained from the same animal. Transport of intact BSA into the intestinal lumen was a saturable process, with a Vmax of 251 +/- 13 ng.cm-2.h-1 and a Km of 0.72 +/- 0.1 mg.mL-1, and represented 7% of the total BSA flux into the intestinal lumen. In the presence of NaF (2 x 10(-3) M), transport of both intact and total BSA was significantly inhibited (intact: control 374 +/- 80 vs. NaF 46 +/- 11, 88% inhibition; total: control 3288 +/- 296 vs. NaF 2550 +/- 235 ng.cm-2.h-1, 22% inhibition; p < 0.05). In addition, colchicine significantly inhibited intact BSA transport (control 339 +/- 15 vs. colchicine 206 +/- 13 ng.cm-2.h-1, 39% inhibition; p < 0.05). TTX had no effect on intact BSA flux. The findings suggest that transport of intact BSA from the serosa into the intestinal lumen is a saturable, energy-dependent process, which involves microtubules but is not under neural regulation.

摘要

肠道被认为是血清蛋白分解和清除的主要部位。大分子从浆膜转运至肠腔的机制尚不清楚。本研究旨在描述白蛋白从浆膜到黏膜的转运特征。使用去除派尔集合淋巴结的剥离大鼠空肠，在短路的尤斯灌流小室中评估牛血清白蛋白（BSA）的转运。为了确定白蛋白从浆膜到黏膜转运的动力学，将浆膜表面暴露于不同浓度（0.5 - 5 mg·mL-1）的BSA中。随时间对黏膜腔室的液体进行采样，并通过酶联免疫吸附测定法（ELISA）检测免疫完整的BSA。所有后续实验均采用冷BSA浓度（2 mg·mL-1），该浓度可产生最大水平的完整BSA转运。为了评估总BSA转运（完整BSA加上降解的BSA），除了2 mg·mL-1冷BSA外，还向浆膜表面添加了10微居里（1居里 = 37吉贝可）的125I标记的BSA。为了进一步描述BSA转运，用氟化钠（NaF）（代谢抑制剂）或秋水仙碱（微管聚合抑制剂）或神经阻滞剂河豚毒素（TTX）处理组织。所有使用抑制剂进行的实验均在从同一动物获取的配对组织中进行。完整BSA向肠腔的转运是一个可饱和的过程，Vmax为251 ± 13 ng·cm-2·h-1，Km为0.72 ± 0.1 mg·mL-1，占进入肠腔的总BSA通量的7%。在存在NaF（2×10-3 M）的情况下完整和总BSA的转运均受到显著抑制（完整：对照374 ± 80 vs. NaF 46 ± 11，抑制率88%；总：对照3288 ± 296 vs. NaF 2550 ± 235 ng·cm-2·h-1，抑制率22%；p < 0.05）。此外，秋水仙碱显著抑制完整BSA的转运（对照339 ± 15 vs. 秋水仙碱206 ± 13 ng·cm-2·h-1，抑制率39%；p < 0.05）。TTX对完整BSA通量无影响。这些发现表明，完整BSA从浆膜到肠腔的转运是一个可饱和的、能量依赖的过程，该过程涉及微管，但不受神经调节。