BIOTIN TRANSPORT IN A HUMAN INTESTINAL EPITHELIAL-CELL LINE (CACO-2)

The apical (AP)-to-basolateral (BL) transport of [H-3]biotin across Caco-2 cell monolayers grown on a Transwell(TM) polycarbonate membrane was shown to be dependent on days in culture, reaching a maximum at 10 days. The AP-to-BL transport of [H-3]biotin was always much greater than the BL-to-AP transport. AP-to-BL transport of [H-3]biotin was concentration- (K(m) = 1.49 muM and V(max) = 1.86 pmol.mg protein-1.minute-1), temperature-, Na+- and energy-dependent, and proceeded against a concentration gradient in the BL side. [H-3]Biotin transport was inhibited by unlabeled biotin and several structural analogues (e.g., desthiobiotin and biotin methyl ester) but not by taurocholic acid. No metabolism of [H-3]biotin was detected in the AP-to-BL transport across Caco-2 cell monolayers. This study demonstrates that [H-3]biotin transport in Caco-2 cells occurs by a carrier-mediated process.