title: Reactivation of Ca2+-dependent cytoplasmic contraction in permeabilized cell models of the heliozoon Echinosphaerium akamae.
abstract: Permeabilized cell models of the large heliozoon Echinosphaerium akamae were prepared by treatment with 100 mM EGTA or 1% Triton X-100. When > 10(-6) M Ca(2+) was added to the EGTA-permeabilized cells, axopodial cytoplasm became contracted and several swellings were formed along the axopodial length. Axonemal microtubules remained intact, while higher concentration of Ca(2+) (> 10(-4) M) induced microtubule disassembly and complete breakdown of the axopodia. In Triton-permeabilized cells, cytoplasmic contraction and relaxation of the cell body were induced repeatedly by successive addition and removal of Ca(2+). The contraction did not require ATP, and was not inhibited by cytochalasin B. Electron microscopy showed, in EGTA-permeabilized axopodia, contractile tubules became granulated by the addition of Ca(2+). From these observations, it is strongly suggested that Ca(2+)-dependent granulation of the contractile tubules is responsible for the axopodial contraction.
authors.affiliation: Department of Biology, Faculty of Sciences, Kobe University, Japan. arikawa@biol.sci.kobe-u.ac.jp
authors.forename: Mikihiko
authors.initials: M
authors.lastname: Arikawa
authors.forename: Toshinobu
authors.initials: T
authors.lastname: Suzaki
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D003285:Contractile Proteins / Q000187:drug effects / Q000378:metabolism*; D056890:Eukaryota / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008954:Models, Biological; D011554:Pseudopodia / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D002614:Chelating Agents; D003285:Contractile Proteins; D002118:Calcium