Autoradiographic study of sugar and amino acid absorption by everted sacs of hamster intestine

Abstract

Autoradiographs were prepared from frozen sections of evcrted sacs of hamster jejunum which had been incubated in vitro with C 14- or H-labcled sugars and amino acids. When such tissue was incubated in 1 mM solutions of L-valine or L-methionine, columnar absorptive cells at tips of villi accumulated these amino acids to conccntrations ranging from 5 to 50 millimoles per liter of cells. Quantitative data were obtained by microdcnsitomctry of C 14 autoradiographs. Similar, though less striking, results were obtained with thc sugars: galactose, 3-0-methylglucosc, a-mcthylglucoside, and 6-dcoxyglucose. In all cases the marked “step-up” in concentration occurred ncar the brush border of the ccll, and a “stepdown” in concentration occurred at the basal pole of thc cell. Known inhibitors of intcstinal absorption, e.g., phlorizin in the case of sugars, blocked the concentrative step at the luminal border of the absorptive cell. It is inferred from these data that active transport systems for sugars and amino acids reside in the brush border region of the cell. Additional evidence suggests that the basal membranc of the cell may be the site of both a diffusion barrier and a weak transport system dirccted into the cell. © 1965, Rockefeller University Press., All rights reserved.