Uptake of galactose by the epithelial syncytium of Schistosoma mansoni.

A steady-state compartmental analytical solution to radiolabeled galactose fluxes into and out of S. mansoni using a three compartment model is presented. Experiments included phlorizin inhibition, Na+-free incubations and inhibition experiments with glucose and 3-O-methylglucose. The inward rate constants exceeded the outward exchange rates by a factor of 1.55 in females and 1.85 in males. Phlorizin, Na+-free conditions and the other hexoses reduced the inward exchange rates such that net secretion of galactose would be favored since the inward to outward exchange rates were less than unity. In the Na+-free incubations, the outward exchange rate was increased but not in the other experiments. The steady-state Kt values were increased in Na+-free incubations and during inhibitions by glucose and 3-O-methylglucose, but not in response to phlorizin. The size of the exchangeable tissue pool of galactose was decreased in a predictable manner when the exchange rates across the surface epithelial syncytium were reduced by glucose, 3-O-methylglucose, phlorizin and Na+-free incubations. The results were generally consistent with previous findings of stereospecific Na+-coupled uptake of galactose by S. mansoni.