Abstract
The effect of membrane surface potential of the apical side on the intracellular uptake of ionic compounds was investigated using the human colon adenocarcinoma cell line (Caco-2). The transepithelial transport of indolepropionic acid and tryptamine was consistent with the uptake behavior shown by rat intestinal brush-border membrane (BBM) vesicles. Imipramine, which diminished the negative charge of the membrane surface (for both Caco-2 and BBM), acted to increase the uptake of the anionic compounds, indolepropionic acid and ceftibuten, and to decrease that of tryptamine (cationic compound) by both the Caco-2 monolayer and the intestinal BBM vesicles at a pH of 7.5. These results suggest that the effects of membrane surface potential on the permeability of ionic compounds were detectable on the Caco-2 cell line as well as the BBM vesicles. On the other hand, the inhibition of H(+)-linked transport and the stimulation of the surface charge-regulated uptake of ceftibuten have occurred simultaneously on the Caco-2 cell line in the presence of imipramine. It seems that the membrane surface charge (negative) plays an important role in the transport process of ionic compounds across the intestinal epithelium.
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