Permeation and Membrane Transport in Animal Parasites: The Absorption of Glucose by Hymenolepis diminuta

Abstract

Understanding the physiology of tapeworms requires the elucidation of processes of nutrition. Since the tapeworm lacks an alimentary tract of any kind, the only means for entry for food is through the integument. Bathed in a medium of complex composition in the intestine, the tapeworm is directly dependent on processes involving penetration of materials from the environment. Read, Simmons and Rothman (1959) have shown that, in the movement of certain amino acids across the membranes of the tapeworm Calliobothrium from marine elasmobranch fishes, diffusion definitely does not account for the observed phenomena. Read (1955) demonstrated, by electron microscopy, villus-like structures on the surface of tapeworms and suggested that micro-canals observed might be associated with absorptive function. These structures suggest that the integument may be an active organ containing many organelles functional in absorption. Much work has been published dealing with the uptake of glucose by red blood cells, isolated loops of intestine, and certain other cells or tissues of vertebrates. The conclusions in each case are generally that the process of diffusion cannot alone account for the results obtained. Various theories have been presented as to the mechanism. In some cases, the energy derived from the metabolic processes probably is required for the uptake of glucose by the tissue to occur; while, in other cases, little work is performed and negligible amounts of metabolic energy seem to be required. In determining whether glucose permeation occurs by diffusion or by a catalytic process (either active transport or facilitated diffusion) rigorous experimental analysis is necessary. The criteria appropriate to such an analysis have been reviewed by Read et al (1959). In the experiments, the results of which are reported in this paper, an attempt was made to ascertain the nature of glucose permeation in a tapeworm. The effects of potassium ion concentration, the relative uptake rates at various stages in the development of the worm, and the effect of worm size on the rate of uptake of glucose have also been studied.