The mechanochemical basis of amoeboid movement: I. Ionic requirements for maintaining viscoelasticity and contractility of amoeba cytoplasm

Glycerination of intact specimens and of isolated cytoplasm of Chaos carolinensis has permitted identification of the requirements for Ca 2+- and Mg 2+-ATP for contraction. The observed loss of some calcium sensitivity during glycerination could be explained as a combination of the extraction of an unidentified calcium sensitive factor(s), low substrate (Mg 2+-ATP) contractions, or a loss of polymerizable actin. In addition, the “rigor” condition induced by complete glycerination destroyed the ability of isolated cytoplasm to stream. Decreases in cytoplasmic birefringence, in visible fibrils and in cytoplasmic contractility were observed both in glycerinated cytoplasm and in freshly isolated cytoplasm after incubation in solutions containing mM concentrations of EGTA. These results suggest that filament disassembly could be involved in the loss of birefringence and contractility of cytoplasm at low divalent cation concentrations. Furthermore, it is suggested that filament disassembly could be involved in cytoplasmic streaming if the free Ca 2+ concentration were lowered below ca 1.0 × 10 −7 M by an efficient calcium sequestering system.