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Ca2+-dependent cytoplasmic contractility of the heliozoon Actinophrys sol

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A “contractile tubules structure (CTS)” has been described in the radiating axopodia and cytoplasm of the heliozoon Actinophrys sol. Permeabilized cell models with fully-extended axopodia were prepared with 100 mM EGTA. When Ca2+ was added to the permeabilized cells, cytoplasmic swellings formed along the length of axopodia in a concentration-dependent manner. Triton X-100 was also used to prepare cell models of heliozoa. In the Triton-extracted cell model, axopodia were detached, but the cell body remained as a mass of cytoplasm which showed repetitive contraction and relaxation in a Ca2+-dependent manner with 10–8 M as its threshold level. A cell homogenate of A. sol was found to yield a precipitate following the addition of Ca2+. Formation of the precipitate occurred within a few minutes after the addition of Ca2+, and was dependent on the concentration of Ca2+. Electron microscopy showed that the CTS-like filamentous structures were present in the cell homogenate, and that the precipitate obtained from the cell homogenate by adding Ca2+ was composed of granular aggregates morphologically similar to the transformed CTS observed after axopodial contraction.

Keywords: Cell model; Contractile tubules; Heliozoa; Permeabilization; Protozoa

Document Type: Original Article


Affiliations: 1: Department of Biology, Faculty of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan; 2: Department of Physiology, Faculty of Medicine, Hiroshima University, Minami-ku, Hiroshima 734–8511, Japan

Publication date: 2002-12-01

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