MEMBRANE TRANSPORT AND METABOLISM OF INOSITOL BY HYMENOLEPIS DIMINUTA (CESTODA)

Abstract

Myoinositol and scylloinositol have been identified qualitatively and quantitatively by gas-liquid chromatography in the cestode worm Hymenolepis diminuta. No myoinosos-2 can be detected. Myoinositol is unevenly distributed throughout the worm; the scolex and germinative region contains more free and phosphatidyl-bound inositol than the more posterior proglottids. This region also contains more lipid-bound phosphorus, less lipid and less water. Myoinositol absorption is more rapid in this anterior region. The absorption of myoinositol by Hymenolepis diminuta involves diffusion at high substrate concentrations and mediated transport at low substrate concentrations. The mediated transport process exhibits saturation kinetics with V(,max) and Kt being 0.0105 (mu)moles/g ethanol extracted dry wt/4 min and 0.0067 mM, respectively. It is sensitive to changes in temperature, pH and sodium ion concentration. D-glucose is a non-competitive inhibitor of myoinositol transport but myoinositol has no effect on D-glucose absorption. Phlorizin interacts competitively with the myoinositol transport system. Various sugar alcohols and amino acids examined have no effect on myoinositol transport. Absorbed myoinositol is incorporated into lipid as phosphatidylinositol but not metabolized to form any other water soluble component. The possible function of inositol in Hymenolepis diminuta is discussed