Thwaites D T, McEwan G T, Brown C D, Hirst B H, Simmons N L
Department of Physiological Sciences, University of Newcastle upon Tyne, Medical School, UK.
J Membr Biol. 1994 Jun;140(2):143-51. doi: 10.1007/BF00232902.
In human Caco-2 intestinal epithelial layers, L-alanine absorption can be energized by a proton gradient across the brush-border membrane. Acidification of the apical medium, even in Na(+)-free media, is associated with a saturable net transepithelial absorption of L-alanine. L-Alanine transport causes cytosolic acidification consistent with proton/amino acid symport. L-Alanine transport in Na(+)-free media is rheogenic, stimulating an inward short-circuit current in voltage-clamped epithelial monolayers. By measurement of rapid L-alanine influx across the apical membrane, L-alanine-stimulated inward short-circuit current and intracellular acidification in the same cell batch, we estimate L-alanine/proton stoichiometry to be 1:0.62 +/- 0.25 (SD) (short-circuit current) or 1:0.73 +/- 0.19 (intracellular acidification). From competition studies, it is likely that L-proline, alpha-aminoisobutyric acid, and beta-alanine, but not L-valine and L-serine, are substrates for proton-linked, substrate transport in the brush border of Caco-2 cells.
在人Caco-2肠上皮层中，L-丙氨酸的吸收可由跨刷状缘膜的质子梯度提供能量。顶端培养基的酸化，即使在无钠培养基中，也与L-丙氨酸的可饱和净跨上皮吸收有关。L-丙氨酸转运导致胞质酸化，这与质子/氨基酸同向转运一致。在无钠培养基中L-丙氨酸的转运是生电的，可刺激电压钳制的上皮单层中的内向短路电流。通过测量L-丙氨酸跨顶端膜的快速流入、L-丙氨酸刺激的内向短路电流以及同一批细胞中的细胞内酸化，我们估计L-丙氨酸/质子化学计量比为1:0.62±0.25（标准差）（短路电流）或1:0.73±0.19（细胞内酸化）。从竞争研究来看，L-脯氨酸、α-氨基异丁酸和β-丙氨酸可能是Caco-2细胞刷状缘中质子偶联底物转运的底物，而L-缬氨酸和L-丝氨酸不是。
