Polarized transport was observed not in hydrophilic compounds but in dextran in Caco-2 cell monolayers.
We examined the efflux from the basal to apical side of fluorescein isothiocyanate-labeled dextran 4000 (FD-4) in Caco-2 cell monolayers using a diffusion chamber system. The permeation clearance (Pm) of FD-4 from the basal to apical side was 6 times greater than that from the apical to basal side at 37 degrees C. Such polarized efflux of FD-4 was evident at 37 degrees C, but not at 4 degrees C. Efflux of FD-4 was dose-dependently inhibited by colchicine, an endocytosis inhibitor. Adding an excess of unlabeled dextran (M.W. 10,000 Da) decreased the efflux of FD-4. On the other hand, transepithelial electrical resistance (TEER) did not change during the experiments under any conditions. These results suggest that the efflux of FD-4 across Caco-2 cell monolayers is apparently mediated by at least two polarized, energy requiring transport systems, one of which shows substrate specificity for dextran polysaccharides.
Tomita
M
M
Department of Biopharmaceutics, School of Pharmacy, Tokyo University of Pharmacy and Life Science, Hachioji, Japan.
Hotta
Y
Y
Ohkubo
R
R
Awazu
S
S
D001692:Biological Transport; D018938:Caco-2 Cells; D016764:Cell Polarity / Q000502:physiology*; D003078:Colchicine / Q000494:pharmacology; D006801:Humans; D008657:Metabolic Clearance Rate; D012995:Solubility; D013379:Substrate Specificity; D014867:Water / Q000737:chemistry
D014867:Water; D003078:Colchicine