Transintegumental Glucose Uptake in Schistosomatium douthitti

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Abstract
The double internal standard isotope method (utilizing both a highly diffusible [3H water] and a nondiffusible reference isotope [113mIn bound to EDTA]) was applied in studies of 14C glucose uptake in the rodent blood fluke, S. douthitti. Uptake of 14C-L-glucose was minimal and occurred by a diffusional mechanism alone. Transintegumental uptake of the stereoisomer 14C-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 .cntdot. min-1 .cntdot. mg wet wt-1) and diffusional component (Kd = 0.57 .mu.l .cntdot. min-1 mg wet wt-1). In females, these measurements (Km = 1.8 .+-. 1.4 mM; Vmax = 11.3 .+-. 2.2 nmol .cntdot. min-1 .cntdot. mg wet wt-1; and Kd = 0.60 .mu.l .cntdot. min-1 .cntdot. 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.

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