Immunocytochemical localization of the intrinsic factor-cobalamin receptor in dog-ileum: distribution of intracellular receptor during cell maturation.
Immunocytochemical localization of the intrinsic factor-cobalamin receptor in dog-ileum: distribution of intracellular receptor during cell maturation.
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狗回肠中内因子钴胺素受体的免疫细胞化学定位：细胞成熟过程中细胞内受体的分布。
DOI：
10.1083/jcb.98.3.1111
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发表时间：
1984
期刊：
影响因子：
--
通讯作者：
Seetharam,B
中科院分区：
文献类型：
--
作者：
Levine,JS;Allen,RH;Alpers,DH;Seetharam,B
内因子钴胺素复合物 (IF-cbl) 与回肠中特定受体的结合促进钴胺素的吸收。这种配体-受体结合反应的物理和生化特征已被广泛研究，但对受体合成、细胞内转运和微绒毛表面膜表达的细胞机制知之甚少。我们试图通过使用超微结构免疫细胞化学将 IF-cbl 受体定位于从麻醉狗的回肠获得的粘膜活检的隐窝、绒毛中段和绒毛尖端区域来描绘这些机制。在开始回肠定位研究之前，我们的研究中使用的纯化犬 IF-cbl 受体的抗血清被证明具有位点特异性（例如，回肠肠上皮细胞与胃肠道内的其他细胞）和免疫组织化学特异性。内质网中的受体合成始于隐窝肠细胞，但在整个绒毛的细胞中继续合成。在绒毛中部区域，合成的受体以载体方式转移至与膜性囊泡相关的微绒毛表面，然后插入微绒毛凹坑中。受体仍然固定在微绒毛坑上，并且不均匀分布在刷状缘膜上。所有绒毛尖端肠上皮细胞在微绒毛凹坑、囊泡和内质网中均含有 IF-cbl 受体，但此外，广泛的核周膜染色以及与多泡体相关的重新内化受体是明显的。绒毛任何水平的基底外侧膜均不含受体。这些观察结果表明 IF-cbl 受体 (a) 通过囊泡转运易位至中绒毛区域的顶端细胞表面，(b) 直接插入并固定在微绒毛凹坑中，(c) 在绒毛尖端细胞的管腔表面上最广泛地表达，以及 (d) 尽管重新内化，但不会将 IF 和/或 cbl 移动至基底外侧细胞表面。膳食中的钴胺素（维生素 B、2、cbl'）需要 Cbl 和内因子 (IF) 的复合物与回肠中的特定受体结合。 IF-cbl 复合物与受体的结合不需要能量，但需要 Ca2+ 和中性 pH (1-3)。我们最近证明 (4) IF-cbl 仅
Absorption of Cobalamin is facilitated by the binding of the intrinsic factorcobalamin complex (IF-cbl) to specific receptors in the ileum. The physical and biochemical characteristics of this ligand-receptor binding reaction have been extensively studied, but little is known about the cellular mechanisms or receptor synthesis, intracellular transport, and expression on the microvillus surface membrane. We attempted to delineate these mechanisms by using ultrastructural immunocytochemistry to localize the IF-cbl receptor in the crypt, mid-villus, and villus tip regions of mucosal biopsies obtained from the ileum of anesthetized dogs. Prior to initiating the ileal localization studies, the antisera to purified canine IF-cbl receptor that was employed in our studies was shown to have specificity for site (eg, ileal enterocytes vs. other cells within the gastrointestinal tract) and immunohistochemical specificity. Receptor synthesis in endoplasmic reticulum begins in crypt enterocytes, but continues in cells throughout the villus. In the mid-villus region synthesized receptor translo-Cates vectorially to the microvillus surface associated with membranous vesicles and then inserts into the microvillus pit. Receptor remains fixed to the microvillus pit and does not distribute uniformly over the brush border membrane. All villus tip enterocytes contained IF-cbl receptor in microvillus pits, vesicles, and endoplasmic reticulum, but in addition extensive perinuclear membrane staining was evident as well as re-internalized receptor associated with multivesicular bodies. Basolateral membranes contained no receptor at any level of the villus. These observations suggest that the IF-cbl receptor (a) translocates to the apical cell surface at the mid-villus region by transport in vesicles,(b) directly inserts into and then remains fixed in microvillus pits,(c) is elaborated on the luminal surface most extensively in villus tip cells, and (d) although reinternalized, does not move IF and/or cbl to the basolateral cell surface.In adult mammals the absorption of physiologic quantities of dietary cobalamin (vitamin B, 2, cbl') requires that a complex of cbl and intrinsic factor (IF) bind to specific receptors in the ileum. The binding ofthe IF-cbl complex to the receptor does not require energy, but does need Ca" and a neutral pH (1-3). We have recently demonstrated (4) that IF-cbl only