Hysteresis of Contraction-Extension Cycle of Glycerinated Vorticella

SYNOPSIS. The helical coiling state of a glycerinated stalk in the family Vorticellidae had been regarded, without any evidence, as a reversible and completely equilibrated mechano-chemical system regulated by the external free Ca²⁺ concentration. Our present detailed observations of many individual stalks of glycerinated Vorticella convallaria revealed that the contraction-extension cycle of the helical stalks caused by increasing and decreasing free Ca²⁺ concentrations in the medium represents a kind of hysteresis. This phenomenon was observed in extensively glycerinated Vorticella in a medium of very low or physiological ionic strength, as well as in briefly glycerinated ciliates. With regard to the configurational change in various parts of a glycerinated stalk during the contraction-extension cycle, it was found that the initial bending of the stalk caused by increasing free Ca²⁺ concentration begins to take place near the zooid (head) while the initial reextension of the stalk with decreasing free Ca²⁺ concentration begins to take place near the zooid (head) while the initial reextension of the stalk with decreasing free Ca²⁺ concentration takes place simultaneously throughout the entire stalk. The Ca²⁺ threshold for complete reextension of the part of the stalk near the rootlet was found to be much higher than that near the zooid.