title: Axopodial contraction in the heliozoon Raphidiophrys contractilis requires extracellular Ca2+.
abstract: Axopodial contraction of the centrohelid heliozoon Raphidiophrys contractilis was induced by mechanical or electrical stimulation. For inducing contraction, extracellular Ca(2+) was required. The threshold level of extracellular Ca(2+) was between 10(-6)-10(-7) M. The speed of axopodial contraction was faster than 3.0 mm/sec. Re-elongation of axopodia started just after contraction, and its initial velocity was approximately 0.30 microm/sec. Electron microscopic observations were carried out using an improved fixative that contained 1 mg/ml ruthenium red and 15 microM Taxol. This fixative prevented artificial retraction of axopodia and resulted in better fixation. A bundle of hexagonally-arranged microtubules was observed in each axopodium, but no other filamentous structures were detected, suggesting that the contractile machinery of axopodia in R. contractilis may be different from that in actinophryid heliozoons in which Ca(2+)-dependent contractile filaments are employed for contraction.
authors: Department of Biology, Faculty of Science, Kobe University, Kobe, Japan.
authors: S M Mostafa Kamal
authors: SM
authors: Khan
authors: Mikihiko
authors: M
authors: Arikawa
authors: Gen
authors: G
authors: Omura
authors: Yasutaka
authors: Y
authors: Suetomo
authors: Soichiro
authors: S
authors: Kakuta
authors: Toshinobu
authors: T
authors: Suzaki
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002413:Cations, Divalent; D004558:Electric Stimulation; D056890:Eukaryota / Q000166:cytology* / Q000502:physiology; D006652:Histological Techniques; D007564:Japan; D008854:Microscopy, Electron; D009068:Movement / Q000502:physiology*; D011554:Pseudopodia / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D002413:Cations, Divalent; D002118:Calcium