Yamashita F, Kim K J, Lee V H
Department of Pharmaceutical Sciences, University of Southern California, Los Angeles 90033, USA.
Pharm Res. 1998 Jul;15(7):979-83. doi: 10.1023/a:1011957506181.
To determine the functional presence ofa H+/peptide cotransport process in rabbit tracheal epithelial cell layers cultured at an air-interface and its contribution to transepithelial dipeptide transport.
Rabbit tracheocytes were isolated, plated on Transwells, and cultured at an air-interface. After 5 or 6 days in culture, uptake and transepithelial transport of carnosine were examined.
Carnosine uptake by tracheocytes was pH-dependent and was saturable with a Michaelis-Menten constant of 170 microM. Moreover, carnosine uptake was inhibited 94% by Gly-L-Phe, 28% by beta-Ala-Gly, but not at all by Gly-D-Phe or by the amino acids beta-Ala and L-His. Unexpectedly. transepithelial carnosine transport at pH 7.4 (i.e., in the absence of a transepithelial pH gradient) was similar in both the apical-to-basolateral (ab) and basolateral-to-apical (ba) directions. Lowering the apical fluid pH to 6.5 reduced ab transport 1.6 times without affecting ba transport, consistent with predominantly paracellular diffusion of carnosine under an electrochemical potential gradient.
The kinetic behavior of carnosine uptake into cultured tracheal epithelial cell layers is characteristic of a H+-coupled dipeptide transport process known to exist in the small intestine and the kidney. Such a process does not appear to be rate-limiting in the transport of carnosine across the tracheal epithelial barrier.
确定在气液界面培养的兔气管上皮细胞层中H⁺/肽共转运过程的功能存在及其对跨上皮二肽转运的贡献。
分离兔气管细胞，接种于Transwells上，并在气液界面培养。培养5或6天后，检测肌肽的摄取和跨上皮转运。
气管细胞对肌肽的摄取呈pH依赖性，且具有饱和性，米氏常数为170μM。此外，甘氨酰-L-苯丙氨酸可抑制94%的肌肽摄取，β-丙氨酰-甘氨酸可抑制28%，但甘氨酰-D-苯丙氨酸或氨基酸β-丙氨酸和L-组氨酸对其无抑制作用。出乎意料的是，在pH 7.4时（即不存在跨上皮pH梯度时），肌肽在顶侧到基底侧（ab）和基底侧到顶侧（ba）方向的跨上皮转运相似。将顶侧液体pH降至6.5可使ab转运降低1.6倍，而不影响ba转运，这与在电化学势梯度下肌肽主要通过细胞旁扩散一致。
培养的气管上皮细胞层对肌肽摄取的动力学行为是小肠和肾脏中已知的H⁺偶联二肽转运过程的特征。这样的过程在肌肽跨气管上皮屏障的转运中似乎不是限速因素。
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