Transintegumental Uptake of Metabolic Substrates in Male and Female Schistosoma mansoni

Abstract

A new method for measuring transintegumental uptake in living schistosomes in vitro has been applied to the study of individual males and females. Uptake of a 14-C labeled test metabolite was compared to that of tritiated water (a highly diffusible reference substance). Use of the short half-life (T 1/2 = 100 min) isotope 113m-Indium, bound to EDTA (ethylene diamine tetra-acetic acid, a nondiffusible reference substance) permitted quantification of the relative amount of 14-C test substance passively adhering to the schistosoma surface. Substraction of this amount provided an estimate of net uptake. D-glucose uptake, as measured by this method, increased with time, approaching equilibrium by two min; a positive correlation between temperature and glucose uptake was also observed. Nondialyzable components in rat, human, horse and fetal calf sera did not enhance glucose uptake. In both male and female schistosomes, minimal uptakes were seen for the nonmetabolizable sugar alcohol mannitol (MW = 182). L-glucose uptake was similarly low, but high uptakes were observed in both sexes for D-glucose. In addition to confirming the stereospecificity of hexose uptake, these studies suggested our technique provides a sensitive method for measurement of both high and low uptake compounds. The uptakes of D-glucose and the L-amino acids--arginine, ornithine, lysine, histidine, phenylalanine and serine--were comparatively higher in female than male schistosomes. Slight elevations in uptake by females were observed for threonine, valine and glycine, but aspartate uptake was slightly higher in males. No dramatic male-female differences were immediately apparent for the uptakes of proline, leucine, isoleucine, tyrosine and glutamate. Schistosomal uptake of L-amino acids that are essential for vertebrates was generally higher than uptake of the nonessential amino acids.