A Model System for Transcellular Active Transport

Abstract

Oxender and Christensen¹ have proposed that the achievement of transcellular transport of amino-acids and sugars against concentration differences is a consequence of intracellular accumulation. Intestinal mucosal cells will accumulate certain sugars during absorption in vitro. McDougal, Little and Crane² have shown that, during the absorption of D-galactose by hamster intestine, the sugar concentration is greatest in the epithelial layer. Similar conclusions were also drawn for galactose and 3–O–methyl-glucose by Kinter and Wilson^3,4 from autoradiographic studies of hamster intestine. On the basis of their findings that the cells in the crypts of Lieberkühn also exhibit an intracellular accumulation of sugar, Kinter and Wilson suggest that, in the intestine, an intracellularly directed sugar pump “is present along the entire cell membrane, the net movement from lumen to blood being due to the far greater surface area because of the microvilli at the luminal border of the cell”⁴.