Morphological Changes During Conoid Extrusion in Toxoplasma Gondii Tachyzoites Treated With Calcium Ionophore

J Struct Biol. 2001 Dec;136(3):181-9. doi: 10.1006/jsbi.2002.4444.


Treatment of tachyzoites of Toxoplasma gondii with the calcium ionophore A23187 induced dramatic ultrastructural changes that were observed by light and electron microscopy. Light microscopy showed a higher percentage (22%) of tachyzoites with the conoid extruded when compared to control parasites. Electron microscopy confirmed the conoid extrusion by both transmission and scanning electron microscopy. Freeze-fracture replicas showed that the plasma membrane adjacent to cytoplasmic dense granules appeared devoid of intramembranous particles. Membrane-limited vesicles and filopodium-like structures at the cell surface were observed in treated cells. 3-D reconstruction from serial sections confirmed the data and showed a heterogeneity in dense granule shape not reported in control cells.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcimycin / pharmacology*
  • Cell Membrane / ultrastructure
  • Freeze Fracturing
  • Image Processing, Computer-Assisted
  • Intracellular Membranes / ultrastructure
  • Ionophores / pharmacology
  • Microscopy, Electron
  • Toxoplasma / drug effects
  • Toxoplasma / physiology
  • Toxoplasma / ultrastructure*


  • Ionophores
  • Calcimycin