Taenia crassiceps: absorption of hexoses and partial characterization of Na + -dependent glucose absorption by larvae

The uptake of ¹⁴C-fructose by T. crassiceps larvae was linear with respect to concentration. Uptake of 0.05 mM¹⁴C-fructose was not inhibited by 5.0 mM unlabeled fructose, tagatose, or sorbose. Fructose appears to enter larvae by diffusion only. The uptake of radioglucose and radiogalactose was not linear with respect to concentration at low substrate concentrations; at high substrate concentrations, the uptake of both hexoses was linear with respect to concentration. Inhibitor studies indicated that both glucose and galactose enter larvae by a combination of diffusion and a mediated process, and that these hexoses are mutually competitive inhibitors of one another. The uptake of glucose and galactose was also inhibited by α-and β-methyl glucoside, fucose, and phlorizin, but not by several amino acids, certain sugar analogs, nor ouabain. Glucose transport is Na⁺ sensitive; K⁺ was demonstrated to be a competitive inhibitor of Na⁺ activation of glucose uptake. After a 90-min incubation in 5 mM unlabeled glucose, larvae accumulated glucose against an apparent concentration difference. Although larvae appear freely permeable to ouabain, this compound had no apparent effect on glucose accumulation. The results of this study are compared with previous studies on Hymenolepis diminuta, Calliobothrium verticillatum, Hydatigera (Taenia) taeniaeformis, and mammalian systems.