Intestinal transport of sugar and aromatic amino acids in killifish, Fundulus heteroclitus

Abstract

Studies with everted intestinal sacs of klllifish, Fun-duhis heteroclitus, have shown that D-glucose, D-galactose, 3-O-methyl-D-glucose (3MG), L-mannose, and L-xylose were transported from mucosal to serosal side against a concentration gradient, whereas L-glucose, D-mannose, D-xylose, [alpha]-methylglucoside, sorbose, and fructose were not transported. It was also found that the aromatic amino acid derivatives, L-tryptophan, L-tyrosine and its meta- and orthoisomers, and 3-NH2-DL-tyrosine were transported across the mucosal membrane, but no transport was observed with D-tryptophan and N-acetyl-L-tryptophan. The transport of D-galactose and L-tryptophan was temperature dependent and was inhibited by DNP and NaN3. At a concentration of 10 m[image] L-phenylalanine reduced the transport of L-tryptophan but not that of galactose. Phloridzin and phloretin at a concentration of 5 x 10-5 [image] greatly inhibited the transport of galactose but exerted either no effect or stimulated the transport of L-tryptophan. Although there was no transport of L-ghicose from mucosal to serosal side, studies with noneverted sacs showed that the final mucosal concentration of L-glucose was greater than the initial concentration, and this increase was abolished by DNP suggesting an intestinal secretion of L-glucose by killifish.