The Role of Calcium and Magnesium Ions in Invasiveness of Schistosome Cercariae

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Abstract
Summary Vital staining of pre-acetabular gland contents of Schistosoma mansoni cercariae by Alizarin Red S, the reversal or inhibition of this staining by Versene (EDTA), and selective staining of these glands with Glyoxal-bis (2 hydroxyanil) (or GBHA), is evidence of the presence of calcium ions therein. Whereas the GBHA technique employed is highly specific for Ca++, Versene and Alizarin Red S are not. The purplish color of ARS-stained glands indicates that their contents are at an alkaline pH before extrusion into the more neutral or acidic surrounding medium. This correlates with previous findings that the cercariae enzymes are most active in an alkaline range. Similar evidence of calcium in pre-acetabular gland contents of Schistosomatium douthitti cercariae is also presented. The decrease in cercarial invasiveness noted as a consequence of metal chelation correlated well with earlier reports of an inhibiting effect of chelating agents on penetration by S. mansoni cercariae, and on the activity of cercarial enzymes. A similar direct correlation between previously described effects of various ions on in vitro activity of extracted cercarial enzymes, and effects of these ions on penetration of S. mansoni cercariae—notably the potentiation of enzyme activity and penetrating ability by Ca++ and Mg++—has also been noted. Addition of Ca++ or Mg++ partially restored the penetrating ability of S. mansoni cercariae exposed to a chelating agent. Calcium chelation by Versene and Alizarin Red S similarly reduced invasiveness of S. douthitti cercariae. These data suggest first, that calcium ions in the pre-acetabular glands of S. mansoni cercariae function in a manner similar to that of a coenzyme or activator to lytic apo-enzymes contained therein, and also that in this capacity, calcium and/or magnesium ions are essential for successful invasion of the definitive host. It is suggested that differences in quality and quantity of heavy metal ions in natural waters may explain some of the variability found in schistosome infections from different laboratories as well as differences in intensities of infection in different endemic areas.