Tegumental Carbohydrate Transport in Intestinal Helminths: Correlation between Mechanisms of Membrane Transport and the Biochemical Environment of Absorptive Surfaces

The properties of the tegumental hexose transport systems of the intestinal helminths Hymenolepis diminuta (Cestoda: Cyclophyllidea) and Moniliformis dubius (Acanthocephala) are described and compared to those of the glucose transport systems of other tapeworm species and of the mucosal brush border of the vertebrate intestine. Glucose transport and accumulation in H. diminuta and in other cestodes are Na+-dependent and K+- and phlorizin-sensitive, and the tegumental glucose transport loci have substrate specificities very similar to those of the vertebrate intestinal mucosa. In contrast, glucose transport across the tegumental surface of M. dubius is neither Na+-dependent nor phlorizin-sensitive, and the substrate specificities of the facilitated diffusion systems for hexose transport in the tegument of this acanthocephalan are markedly different from those observed for the concentrative transport systems of the H. diminuta tegument and of the host intestinal mucosa. The accumulation of free glucose pools within the body wall of M. dubius appears to involve the "shuttling" of absorbed glucose through the nonreducing disaccharide trehalose. It is suggested that the differences in mechanisms of glucose transport and accumulation between M. dubius, on the one hand, and the tapeworm tegument and the vertebrate intestinal mucosa, on the other, derive from differences in the cytoarchitecture of these absorptive surfaces which share a common biochemical environment. It is further suggested that Na+-coupled carbohydrate transport against a concentration difference may be a unique feature of tissues whose absorptive surfaces comprise a brush border membrane.