Changes in glucose metabolism and cyanide sensitivity in Schistosoma mansoni during development

Schistosoma mansoni was studied by biochemical and electrophysiological techniques to follow the physiological changes occurring during transformation in the mammalian host. Volume conducted electrical potentials and measurement of CO2 evolution indicate that 3 h post-transformational schistosomula are highly sensitive to cyanide. By 24 h after transformation, evolution of CO2 under control conditions is reduced by 77% from 3 h levels, while lactate excretion rises by 84%. Cyanide does not affect the frequency or magnitude of endogenous electrical transients, but does eliminate 83% of the already reduced levels of CO2 evolved in 24 schistosomula. Electrophysiological analyses indicate that the timecourse of metabolic changes in skin- and mechanically transformed schistosomula are similar, and incubation of schistosomula in 200 micrograms ml-1 puromycin does not alter the onset of cyanide insensitivity. The adult parasite evolves a low level of CO2 which is reduced by 88% in the presence of 1 mM cyanide. No significant Pasteur effect is detected, however, and endogenous electrical activity as well as mechanical responses of the adult musculature are unaffected by cyanide exposure. Our results indicate that schistosomula continue to rely on cyanide-sensitive respiratory components for at least 3 h after transformation; by 24 h, however, the parasites are metabolically similar to the adult stage, i.e., they depend on lactate fermentation for most of their energy requirements.