Sugar Transport by Larval and Adult Proterometra macrostoma (Digenea) in Relation to Environmental Factors

Abstract

Monosaccharide transport systems were identified in rediae and cercariae of Proterometra macrostoma. Glucose transport by cercariae in vitro was accomplished by the bodies, but tails absorbed glucose by diffusion alone. No sugar transport system was detected in adults obtained from laboratory infections of sunfish. Temperature of Elkhorn Creek where infected snails (Goniobasis livescens) were found varies from 28 C in summer to 5 C in winter. Glucose transport by both larval stages was optimal between 30 and 25 C and was negligible below 15 C. Transport by rediae was activated by Na+ and was maximal at 50 mM, the approximate Na+ concentration of snail hemolymph. The redial glucose transport system was inhibited by various sugars and was more sensitive to phlorizin than to phloretin. Rediae accumulated glucose and nonmetabolized 3-O-methyl-glucose against apparent concentration gradients, indicating an active transport system. In contrast, glucose transport by "embryonic" cercariae was completely inhibited by 10 mM Na+. Transport by cercariae aged in creek, water 6 hr became relatively insensitive to Na+, and were less permeable to glucose by diffusion. The cercarial system differed in other characteristics from the redial system, including its high sensitivity to phloretin relative to phlorizin and its lower Vmax. The cercarial system apparently functioned only as a facilitated diffusion system that served to move sugar across the tegument down its chemical gradient. Development of P. macrostoma thus showed functional transformations of the tegument that may be subject to regulation by environmental factors.