Mechanism of 3-0-methylglucose uptake by Hymenolepis diminuta.

The mechanism by which Hymenolepis diminuta (Cestoda) absorbs 3-0-methylglucose (30MG) in vitro was analyzed. Influxes of 0.1 and 0.01 mM-3H-30MG during incubations ranging from 5 s to 60 min were not affected significantly when 10 mM-unlabeled 30MG was present as an inhibitor. After 60 min in 0.1 mM-3H-30MG, the concentration of labeled substrate within tapeworms (0.04 mumol ml-1 worm water = 0.04 mM) was less than that of the bathing medium. Tapeworms incubated for 1 h with either 5 mM-glucose or 5 mM-beta-methylglucose (beta MG) gained 15-20% more water than did tapeworms in saline alone, but addition of 5 mM-30MG to the saline had no significant effect on weight change. When the 3H-30MG concentration was varied from 0.01 to 10 mM, influxes were a linear function of substrate concentrations. These analyses show that H. diminuta absorbs 30MG by simple diffusion alone. Thus, use of this monosaccharide to estimate the internal concentration of actively transported sugars (e.g. glucose or beta MG) in H. diminuta is invalid.