Monographs on fragrance raw materials

Membrane transport in helminth parasites: a review.

Publisher Summary This chapter discusses interaction of helminths and their hosts within the alimentary canal and, especially the stomach and intestines. Many such parasites live in the gastro-intestinal canal while others penetrate into the wall of the canal and a few invade organs, such as the liver and pancreas. The dynamic relationship between parasite and host is clearly shown and a good example set for future researchers. First, there is a study of the parasite–host interface, including the various kinds of organs of attachment, the varied nature of the lumen and the mucosa of the gastrointestinal canal, the nature of adhesion, and absorptive surfaces of the helminth and the host. The chapter describes the ecology of helminth site selection by trematodes, cestodes, and nematodes and matters concerning concurrent infections, transplantation, and migration. The chemical and physical characteristics of the intestinal lumen ionic and osmotic characters, microbial ecology, enzymes, bile acids and dietary fats, nutritive gradients, and matters of luminal homeostasis are discussed. The functional gradients in the gastrointestinal tract, bearing on the absorption of electrolytes and nonelectrolytes, water absorption, and malabsorption are also discussed.

Ecological and Physiological Aspects of Helminth-Host Interactions in the Mammalian Gastrointestinal Canal

Short-chain fatty acid (SCFA) concentrations of intestinal contents from the herbivorous tilapia, Oreochromis mossambicus, were analysed by gas and high-performance liquid chromatography. Concentrations of acetate ranging from 3 to 18 mmol l-1 were found along the full length of the intestinal tract, as were trace amounts of propionate. Characteristics of [3H]acetate transport by the intestinal brush-border membrane were analysed in isolated brush-border membrane vesicles (BBMV). Influx of [3H]acetate into BBMV occurred by apparent anion exchange and was not enhanced by inwardly directed gradients of sodium or potassium, indicating the lack of sodium-dependent coupling for acetate transport. Competition and stimulation studies with various organic and inorganic anions revealed the likelihood of a transport system in which [3H]acetate is exchanged specifically for intracellular bicarbonate or other SCFA. Other anions tested had only limited or negligible effects on [3H]acetate uptake. Kinetic analysis over a concentration range of external acetate from 0.1 to 35 mmol l-1 yielded a carrier transport Km of 6.4 mmol l-1 and a Jmax of 5.3 nmol mg protein-1 10 s-1. Transport of [3H]acetate was not significantly affected by inhibitory drugs specific for anion exchangers. This study suggests that there is a specific antiport system for anions that is shared by bicarbonate and short-chain volatile fatty acids in the intestinal brush-border membrane of this herbivorous teleost.

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Short-chain fatty acid transport in the intestine of a herbivorous teleost.

Three species of Siboglinum, two from Norway and one from the Bay of Biscay, were removed from their tubes and exposed to seawater solutions of 14C-labelled phenylalanine, mixed amino acids, glucose, palmitic acid, and sodium butyrate; the range of concentrations used, 10-8 M to 10-5 M, was similar to that reported from seawater and marine sediments. All species accumulated glucose and amino acids, though at different rates. The rate declined with time but the quantity accumulated did not show a plateau effect. Kinetics of uptake suggest that active transport could be involved: Km values are in the range 10-7 M to 10-5 M, at least two orders of magnitude lower than Km values for uptake by vertebrate intestine or intestinal parasites. Fatty acids are accummulated to a lesser extent. Further experiments suggest that the tentacle is not necessary for uptake which takes place in all regions of the body. These species spend most of their time inside their tubes which do not impose a serious barrier to...

Observations on the role of dissolved organic compounds in the nutrition of benthic invertebrates

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.

C. P. Read

Papers

Studies on membrane transport. II. The absorption of acetate and butyrate by Hymenolepis diminuta (Cestoda).