AJP - Gastrointestinal and Liver Physiology, Vol 240, Issue 5 392-G400, Copyright © 1981 by American Physiological Society
Sugar absorption and secretion by winter flounder intestine
R. J. Naftalin and A. Kleinzeller
Transport of sugars by winter flounder (Pseudopleuronectes americanus)
intestine has been examined, and the following observations have been made.
1) No net absorption of D-galactose was found in controls; however,
mucosally applied 0.1 mM phlorizin stimulated the mucosal-serosal flux with
net sugar secretion. 2) Net absorption of methyl glycosides was inhibited
by D-galactose, 0.1 mM ouabain, and phlorizin (without induction of
secretion). 3) Net secretion of 2-deoxy-D-galactose was found without
cellular accumulation of free sugar. The secretory process had a Km of 10
mM and was inhibited by serosally applied 0.1 mM phloretin, bilateral
replacement of Ringer Na+ by choline, serosal ouabain, and D-galactose. 4)
No net absorption or secretion of 2-deoxy-D-glucose was found with a
variety of experimental conditions. 5) At least two active transport
systems for sugars appear to be operative in the flounder intestine: a
conventional Na+-dependent sugar transport system across the brush border
that allows net absorption and a Na+-dependent secretory system that
apparently also operates across the mucosal border. Because D-galactose is
transported by both systems, there is no net flux of this sugar. Several
possible models for the net secretory system are discussed.
