Axopodial Contraction in the Heliozoon Raphidiophrys contractilis Requires Extracellular Ca^<2+>(Cell Biology)

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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 3.0mm/sec. Re-elongation of axopodia started just after contraction, and its initial velocity was 〜0.30μm/sec. Electron microscopic observations were carried out using an improved fixative that contained 1mg/ml ruthenium red and 15μM 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.
社団法人日本動物学会の論文
2003-11-25