Ca2+-dependent nuclear contraction in the heliozoon Actinophrys sol

Cell Calcium. 2005 Nov;38(5):447-55. doi: 10.1016/j.ceca.2005.06.034.


Ca2+-dependent contractility was found to exist in the nucleus of the heliozoon protozoan Actinophrys sol. Upon addition of Ca2+ ([Ca2+]free = 2.0 x 10(-3) M), diameters of isolated and detergent-extracted nuclei became reduced from 16.5+/-1.7 microm to 11.0+/-1.3 microm. The threshold level of [Ca2+]free for the nuclear contraction was 2.9 x 10(-7) M. The nuclear contraction was not induced by Mg2+, and was not inhibited by colchicine or cytochalasin B. Contracted nuclei became expanded when Ca2+ was removed by EGTA; thus cycles of contraction and expansion could be repeated many times by alternating addition of Ca2+ and EGTA. The Ca2+-dependent nuclear contractility remained even after high salt treatment, suggesting a possible involvement of nucleoskeletal components in the nuclear contraction. Electron microscopy showed that, in the relaxed state, filamentous structures were observed to spread in the nucleus to form a network. After addition of Ca2+, they became aggregated and constructed a mass of thicker filaments, followed by re-distribution of the filaments spread around inside of the nucleus when Ca2+ was removed. These results suggest that the nuclear contraction is induced by Ca2+-dependent transformation of the filamentous structures in the nucleus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / pharmacology*
  • Cell Nucleus / drug effects*
  • Cell Nucleus / ultrastructure
  • Egtazic Acid / pharmacology
  • Eukaryota / ultrastructure*
  • Microscopy, Electron
  • Nuclear Matrix / drug effects*


  • Egtazic Acid
  • Calcium