title: Mg2+-dependent stabilization during triton X-100 extraction of Spirostomum followed by calcium reactivation.
abstract: The contractility in the ciliate Spirostomum is regulated by the action of Ca2+ on organized arrays of 60 A microfilaments and microtubules. Contractile cell models of the Protozoa were prepared by treatment with a calcium-free EGTA buffered medium with 0.02% triton X-100 and 20 mMMgCl2. Extracted cells were made to contract when calcium was buffered to greater than 10-5M. Ca2+ removal in the presence of ATP resulted in partial re-extension. The results suggest that the high concentration of Mg2+ functionally stabilizes the contractile elements during extraction. Ca2+ activation can overcome the Mg2+ effect only when the ratio of Mg2+:Ca2+ is less than 10(3).
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000648:ultrastructure; D016798:Ciliophora / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D003599:Cytoskeleton / Q000648:ultrastructure; D004533:Egtazic Acid; D008274:Magnesium / Q000494:pharmacology*; D009068:Movement / Q000187:drug effects*; D011092:Polyethylene Glycols / Q000494:pharmacology*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*
chemical_list: D000644:Quaternary Ammonium Compounds; D011092:Polyethylene Glycols; D004533:Egtazic Acid; D008274:Magnesium; D002118:Calcium