Relationship between transport of D-xylose and other monosaccharides in jejunal mucosa of children.

In order to clarify the relationship between the transport of D-xylose, D-glucose, and Na in human gut, several characteristics of D-xylose uptake were examined in jejunal biopsies from 47 children (45 with normal intestinal function and 2 with glucose-galactose malabsorption). Standard in vitro techniques were used, with the following results: In tissue accumulation experiments with Ringer solution, the intracellular D-xylose concentration (C) was not significantly different from the medium D-xylose concentration (M) (C/M = 1.10 +/- 0.08). D-Xylose uptake was not affected by the disappearance of the Na electrochemical gradient in the presence of ouabain or DNP (C/M = 1.02 +/- 0.16 and 0.96 +/- 0.04, respectively). However, in Na-free solution, D-xylose uptake decreased (C/M = 0.47 +/- 0.08). The influx of 10 mM D-xylose across the luminal membrane (Jmcxyl = 1.34 mumol/h . cm2) was not significantly influenced by 2 mM phlorizin (Jmcxyl - 1.25 mumol/h . cm2), which is a competitive inhibitor of D-glucose transport. Removal of Na from the incubation medium, reduced Jmcxyl by 55%. Galactose (40 mM) and fructose (40 mM) did not inhibit Jmcxyl (2.18 and 2.27 mumol/h . cm2, respectively). In Ussing chambers, D-xylose did not stimulate the short-circuit current (Isc), neither did it interfere with the increase in Isc induced by glucose. In the congenital absence of glucose and galactose active transport, D-xylose entry into the cell was unaltered. These results support the concept that in jejunal mucosa of children, D-xylose is at least in part, transported by a system that is different from those for fructose and Na-dependent D-glucose (hexose) transport.