Localization of facilitated diffusion and active glucose transport in cysticercoids of Hymenolepis diminuta (Cestoda)

Abstract

Active glucose transport by adults of Hymenolepis diminuta is known to be Na +-dependent and more sensitive to phlorizin than to phloretin. We found that infective cysticercoids apparently take up glucose by facilitated diffusion. This type of transport was distinguished by insensitivity to Na + and phlorizin, but inhibition by phloretin. The preferred substrate was glucose followed by galactose > β-methylglucoside > α-methylglucoside; mannose, glucosamine, 3- O-methylglucose, melibiose and 2-deoxyglucose did not interact with the system. V max and K t for glucose transport were 9.9 ±2.46 nmoles 25 larvae/h, and 0.8 ± 0.27 m M , respectively. In an attempt to localize the transporters, the cysticercoid wall enclosing the scolex was removed by excysting the larvae in vitro. Glucose uptake by the excysted scoleces was similar to adult transport, i.e. Na +-dependent and sensitive to phlorizin rather than phloretin. These results indicate that the withdrawn scolex, like the adult, is capable of active glucose transport. Facilitated diffusion appears to be associated primarily with the cyst wall which is lost when the larva excysts in the vertebrate host