Compartmentalization of radioactive glucose in the plerocercus metacestode of Otobothrium insigne (Cestoda: Trypanorhyncha)

Abstract

Otobothrium insigne plerocerci were used to study the compartmentalization of radioactive glucose in a metacestode bladderworm under in vitro conditions. When plerocerci were incubated in C 14-labeled glucose, this glucose was rapidly absorbed by the blastocyst outer-wall tegument. Within minutes, this absorbed glucose diffused through the blastocyst wall and into the blastocyst cavity. Over 95% of the absorbed glucose remained as free glucose in the blastocyst walls and cavity even after 2 h post-incubation. When plerocerci were first pulse-incubated in radioactive glucose for 30 min, and then chase-incubated in glucose-free saline for several days, the quantity of unbound radioactive glucose in the blastocyst walls and cavity decreased significantly during the first 48 h while the quantity in the scolex increased. The radioactivity of the blastocyst wall glycogen and scolex glycogen both increased during this time; however, the scolex incorporated significantly more radioactive glucose into its glycogen than did the blastocyst wall in spite of the wall's larger quantity of endogenous glycogen and its closer proximity to the large glucose pool of the blastocyst cavity. Thus, it appears that under conditions where exogenous glucose concentrations are low, the juvenile scolex takes nutritional precedence over the blastocyst such that glucose is diverted from the blastocyst walls to the scolex in order to maintain carbohydrate steady state conditions in the scolex.