Transintegumental glucose uptake in Schistosomatium douthitti

The double internal standard isotope method (utilizing both a highly diffusible [H3 water] and a nondiffusible reference isotope [113m-indium bound to ethylene diamine tetra-acetic acid]) was applied in studies of C14 glucose uptake in the rodent blood fluke. Schistosomatium douthitti. Uptake of C14-L-glucose was minimal and occurred by a diffusional mechanism alone. Transintegumental uptake of the stereoisomer C14-D-glucose, corrected for passive adsorption of the solute on the external tegumental surface, occurred by a saturable, carrier-mediated mechanism. Kinetic analyses demonstrated that glucose uptake was best described by a carrier system plus a diffusional component. Estimates were derived in male worms for the half-saturation constant (Km - 1.7 +/- 1.0 mM), maximal velocity (Vmax = 10.4 +/- 1.7 nmol.min-1.mg wet wt-1) and diffusional component (Kd = 0.57 microliters.min-1.mg wet wt-1). In females, these measurements (Km = 1.8 +/- 1.4 mM; Vmax = 11.3 +/- 2.2 nmol.min-1.mg wet wt-1; and Kd = 0.60 microliters.min-1.mg wet wt-1) were similar. These parameters were compared with estimates from mammalian tissues, and differences were attributed tentatively to the greater surface area-to-volume ratio of the schistosome.