The rapid development of the glucose transport system in the excysted metacestode of Hymenolepis diminuta

SUMMARYTemporal changes in glucose transport capacity in excysted scoleces ofHymenolepis diminutawere examined. Assays involved incubation for 1 min in [3H]glucose after pre-incubation for 1 min to 8 h in saline. There were two abrupt increases in uptake velocity, a relatively small one between 15 and 75 min, and a large one between 5 and 6 h, during which theVmaxincreased from 0·36 to 2·49 nmol/25 larvae/h. The second increase was unaffected when the pre-incubation saline contained 5 mM glucose, but it was completely blocked when the excysted larvae were pre-incubated in Ca2+-free saline. Abrupt glucose transport changes did not occur in intact cysticercoids or in scoleces when the substrate was [3H]leucine or [3H]uracil. Arrhenius plots (logVversus 1/temperature, 10–42 °C) were linear for intact cysticercoids, but were biphasic for both scoleces and adults with discontinuities at 20 ± 1 °C. Thus, ‘activation’ of the excysted scolex seemed to involve a specific, Ca2+-dependent increase in number of glucose transporters functioning in the worm surface. The Arrhenius plots indicated that development in the final host does not involve a major change in lipid composition of the parasite's membranes.