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Unique precipitation and exocytosis of a calcium salt of myo ‐inositol hexakisphosphate in larval Echinococcus granulosu s
Author(s) -
Irigoín Florencia,
Casaravilla Cecilia,
Iborra Francisco,
Sim Robert B.,
Ferreira Fernando,
Díaz Alvaro
Publication year - 2004
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.20262
Subject(s) - calcium , echinococcus granulosus , biophysics , chemistry , biochemistry , vesicle , transmission electron microscopy , exocytosis , extracellular , ultrastructure , microbiology and biotechnology , secretion , biology , membrane , materials science , anatomy , nanotechnology , zoology , organic chemistry
The ubiquitous intracellular molecule myo ‐inositol hexakisphosphate (IP 6 ) is present extracellularly in the hydatid cyst wall (HCW) of the parasitic cestode Echinococcus granulosus . This study shows that extracellular IP 6 is present as its solid calcium salt, in the form of deposits that are observed, at the ultrastructural level, as naturally electron dense granules some tens of nanometers in diameter. The presence of a calcium salt of IP 6 in these structures was determined by two different electron microscopy techniques: (i) the analysis of the spatial distribution of phosphorus and calcium in the outer, acellular layer of the HCW (the laminated layer, LL) through electron energy loss spectroscopy, and (ii) the observation, by transmission electron microscopy, of HCW that were selectively depleted of IP 6 by treatment with EGTA or phytase, an enzyme that catalyses the dephosphorylation of IP 6 . The deposits of the IP 6 ‐Ca(II) salt are also observed inside membrane vesicles in cells of the germinal layer (the inner, cellular layer of the HCW), indicating that IP 6 precipitates with calcium within a cellular vesicular compartment and is then secreted to the LL. Thus, much as in plants (that produce vesicular IP 6 deposits), the existence of transporters for IP 6 or its precursors in internal membranes is needed to explain the compound's cellular localisation in E. granulosus . © 2004 Wiley‐Liss, Inc.