AJP - Gastrointestinal and Liver Physiology, Vol 238, Issue 4 326-G331, Copyright © 1980 by American Physiological Society
Xylose transport pathways in rabbit ileum
M. Heyman, A. M. Dumontier and J. F. Desjeux
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.
