Tentacle contraction and ultrastructure inDiscophrya collini: The response to cations

Summary Discophrya collini is a suctorian protozoan with contractile tentacles containing a microtubule-lined canal and microfilaments. The effects of a range of cations on tentacle contraction and ultrastructure have been determined. Treatment with 80 mM CaCl₂ and 95 mM MgCl₂ causes contraction to 28% and 57% of the control length respectively. Re-extension takes over 4 hours in the culture medium, but CaCl₂-treated tentacles are re-extended after a 5 minutes treatment with 10^–2 M EDTA or 5 × 10^–3 M EGTA. CuCl₂ causes a significant contraction at 10^–5 M (to 77%); LaCl₃ at 10^–4 M (to 65%); ZnCl₂ at 10^–2 M (to 65%), but BaCl₂, CoCl₂, MnCl₂, NiCl₂, and SrCl₂ cause significant changes only at 10^–1 M.The cytoplasm of CaCl₂-treated cells contains two forms of membraneous structures when viewed in TEM; that of MgCl₂-treated cells reveals granular areas of medium electron density. None of these features are seen in control cells. The microtubules of the tentacle canal appear to be intact upon its retraction into the cell with no change occurring in the numbers or relative positions of the microtubules. The tentacle cortex is wrinkled. It is suggested from this and previous work that tentacle contraction may be mediated by a microfilament-based mechanism, and that calcium may be involved.