On the uptake of biotin by the rat renal tubule

Little is known of biotin handling by transporting epithelium. Accordingly, we have examined the characteristics of biotin uptake by rat renal tubular epithelium. Renal cortical slices showed concentrative, temperature-sensitive uptake of biotin. Renal brushborder membrane vesicles exhibited an "overshoot" phenomenon with uptake of 1.9 nM biotin in the presence of a 100 mM NaCl gradient. This overshoot was reduced in magnitude with reduction of the sodium gradient to 50 mM. Biocytin significantly reduced uptake by the vesicles. Concentration-dependent studies yielded an apparent transport Km of 200 nM. We conclude that biotin is actively transported by the rat renal proximal tubule by a system which is at least partially Na+ dependent, and shared by biocytin.