Abstract

With everted intestinal sacs the intestine of channel catfish was found to transport d-glucose and d-galactose from mucosal to serosal side against a concentration gradient, by a Na⁺-and HCO₃,-dependent, phlorizin- and ouabain-sensitive mechanism. There was no transmucosal transport of 3-O-methyl-d-glucose, l-glucose or l-fucose. Catfish intestine was also found to transport l-tyrosine, against a concentration gradient. In Na-free bathing solution or in the presence of ouabain, the rate of transport of l-tvrosine was reduced to about half of the control value. The transport of this amino acid was inhibited by l-phenylalanine but was unaffected by phlorizin. With the Ussing chamber technique the electrical properties of catfish intestine were found to be closely related to those of winter flounder intestine; a potential difference of 1 to 5 mV was recorded with the serosa being electronegative to mucosa. Isotopic flux measurements revealed a simultaneous transmural transport of Na and Cl ions from mucosal to serosal side. with a net Cl flux greater than the net Na flux.