A New Drag Model for Contracting Vorticella Revealed the Stalk-length-dependence of Vorticella Stalk Contractility

Vorticella is a sessile protozoan, and tis stalk contracts on a millisecond timescale. Because this contraction is induced by the binding of calcium ions, the Vorticella stalk showcases calcium-powered cellular motility. In this study, the contractility of Vorticella cells of various stalk lengths were estimated using a new drag model which took account of the unsteadiness and finite Reynolds number of the water flow generated by contracting Vorticella and the wall effect of Vorticella’s residence substrate. It was found that various key contractility parameters depended on the stalk length, and the observed stalk-length-dependencies were simulated using a damped spring model, which enabled estimating that the spring constant of the contracting stalk. These observed length-dependencies of Vorticella’s contractility appear to reflect the biophysical mechanism of the spasmonemal contraction.