STUDIES ON MEMBRANE TRANSPORT. II. THE ABSORPTION OF ACETATE AND BUTYRATE BY HYMENOLEPIS DIMINUTA (CESTODA)

Abstract

1. At low substrate concentrations (below approximately 2 mM) Hymenolepis diminuta absorbs acetate by a mediated process; at high substrate concentrations the main mode of entry is diffusion. 2. Hydrogen ion concentration affects acetate uptake. At low pH the rate is increased and there is a larger diffusion component. Inhibition of acetate uptake by propionate is depressed at low pH. 3. Acetate uptake is inhibited by other short chain fatty acids but is unaffected by a variety of other compounds. The kinetics of the inhibitions were examined and inhibitions were found to be partially competitive in the case of propionate, butyrate, valerate and octanoate and fully competitive in the case of formate. Butyrate uptake is also inhibited by these compounds. 4. The data are discussed in terms of transport of fatty acids, lipid metabolism in cestodes and possible significance in the ecology of the organism.