Two cationic channels present in the microsomal fraction from Echinococcus granulosus protoscoleces of the sheep strain were studied in planar bilayer reconstitution experiments. A whole-worm homogenate was subjected to differential centrifugation and the postmitochondrial supernatant was laid on the top of a discontinuous sucrose gradient. The 15-30% (w/v) membrane fraction, enriched in NADPH-cytochrome c reductase, exhibited the highest fusion rate, two cationic channels being most frequently reconstituted. Both of them were highly cation-selective and had high conductances (244 and 107 pS in symmetrical 150 mM KCl). In most experiments, none of them displayed voltage dependence. The 244-pS channel was activated by Ca2+ and blocked by Ba2+, both in the micromolar range, thus partially resembling the Ca2+-activated K+ channel from more highly evolved animals. The 107-pS channel exhibited a Cs+ ≅ K+ > Na+ > Li+ > Ca2+ selectivity sequence (as measured by permeability ratios) and, most frequently, a high open probability (>0.9) irrespective of the experimental conditions used, therefore sharing many properties of Schistosoma mansoni outer tegumental membrane cation channels.
ASJC Scopus subject areas
- Infectious Diseases