Tai C Y, Jackson M J
J Membr Biol. 1981 Mar 15;59(1):35-43. doi: 10.1007/BF01870819.
Studies on the intestinal transport of weak acids suggest that the subepithelial tissues exhibit a modest, but significant, ability to discriminate between the ionized and nonionized forms. This suggestion has been tested directly in experiments using an in vitro preparation of rat small intestine from which the epithelial cells were removed, but in which the structural and functional integrity of the subepithelial tissues was maintained. Studies on the effects of potential difference on the fluxes of weak acids in this preparation showed that the ratio of permeabilities for the ionized and nonionized species (Pi/Pni) was indeed less than one, and of a magnitude comparable to the value suggested by analysis of transport in the intact tissue. (Pi/Pni) for the subepithelial tissue decreased as pH was increased, and the discriminatory properties of the tissue were abolished [(Pi/Pni)=1] on treatment with the cationic macromolecule polyethyleneimine (PEI). These observations suggested that the discriminatory properties of the subepithelial tissues were determined by fixed anionic sites, and morphological studies with PEI indicated that such sites were concentrated in the region of the basement membrane.
关于弱酸在肠道转运的研究表明，上皮下组织具有一定能力，虽不显著但能区分离子化形式和非离子化形式。这一观点已在实验中直接得到验证，实验采用大鼠小肠的体外制备物，其中上皮细胞已被去除，但上皮下组织的结构和功能完整性得以维持。对该制备物中电位差对弱酸通量影响的研究表明，离子化和非离子化物种的渗透率之比（Pi/Pni）确实小于1，且其大小与对完整组织转运分析所提示的值相当。上皮下组织的（Pi/Pni）随pH升高而降低，用阳离子大分子聚乙烯亚胺（PEI）处理后，组织的区分特性消失[（Pi/Pni）=1]。这些观察结果表明，上皮下组织的区分特性由固定阴离子位点决定，用PEI进行的形态学研究表明，这些位点集中在基底膜区域。
