Contractile events in the cilia of Paramecium, Opalina, Mytilus, and Phragmatopoma.

The motion of the abnormal cilia of Opalina and Mytilus can be described by the recently developed model for ciliary motion, provided the activation of the contractility during the effective stroke is reduced by three- to fivefold compared with that in the recovery stroke. The stiffness of the Mytilus cilium during the effective stroke is found several hundred times larger than that predicted by the model, however. The stiffness of the cilia of Paramecium, Opalina, Phragmatopoma, and of Mytilus in the recovery phase, is predicted approximately correctly by the model. The activation of contractility in Mytilus and Phragmatopoma cilia increases with the viscosity of the medium, as the velocity of the ciliary motion slows down. This leads to the equivalent of a force-velocity relation. The velocity of propagation of the bend in the cilia during the recovery stroke is shown to be dependent only on the elastic properties of the ciliary shaft, and to be independent of the contractile activiey.