Xylose transport pathways in rabbit ileum.

The D-xylose transepithelial transport mechanism was examined in rabbit ileum in vitro. The net flux of D-xylose (Jxylnet) from mucosa to serosa is abolished in the presence of 10(-4) M ouabain. D-Xylose stimulates the net flux of sodium (JNanet) and the short-circuit current (Isc) equally. The D-xylose concentration at which delta Isc reaches half its maximal value is 70 +/- 5 mM. The steady-state intracellular D-xylose concentration ([X]c) is lower than the extracellular concentration in all the situations examined. However, [X]c is Na dependent. The unidirectional influx across the luminal membrane (Jxyl m leads to c) decreases by 50% in the absence of Na; the Na-dependent Jxyl m leads to c is entirely inhibited by D-galactose (40 mM). However, in the absence of Na, Jxyl m leads to c is not inhibited by D-galactose, D-fructose, D-mannose, 2-deoxy-D-glucose or phloretin. In the absence of Na, J xyl m leads to c is a linear function of extracellular D-xylose concentrations up to 300 mM. In the presence of 10 mM D-glucose, there is a linear relationship between transepithelial D-xylose permeability, and polyethylene glycol (4,000 mol wt) permeability. These results indicate the possible existence of a cellular and a paracellular route for D-xylose and related molecules.