Axopodial contraction in the heliozoon Raphidiophrys contractilis requires extracellular Ca2+.
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.
Khan
S M Mostafa Kamal
SM
Department of Biology, Faculty of Science, Kobe University, Kobe, Japan.
Arikawa
Mikihiko
M
Omura
Gen
G
Suetomo
Yasutaka
Y
Kakuta
Soichiro
S
Suzaki
Toshinobu
T
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
D002413:Cations, Divalent; D002118:Calcium