Cytoplasmic free calcium and amoeboid movement.

Measurements with the Ca2+ -sensitive photoprotein aequorin show that locomotion in the amoeba Chaos carolinense occurs without changes in the aequorin signal and that not more than 0.025% of the cytoplasm can exist at the micromolar threshold concentration for contraction. The results do not support the hypothesis that cytoplasmic streaming is under the control of changes in the cytoplasmic free Ca2+ concentration.