A Novel Type of Ciliary Activity in Stylonychia Mytilus: Analysis of Potential-coupled Motor Responses in the Transverse Cirri

The motor responses of the transverse cirri of Stylonychia mytilus were investigated by applying high-speed microcinematography and step voltageclamp. As a response to hyperpolarization, the transverse cirri began to swing posteriorly from an inactive upright posture at rest. The deeply inclined posture was maintained as long as the hyperpolanzing pulse was on. Upon depolarization, the cirri began to swing towards the anterior end of the cell and continued regular cyclic beating, orienting the effective stroke anteriorly. Motor responses of the transverse cirri occurred in quasi-planar motion, allowing analysis of the bend configuration along the full length of the cirri. Beating activity induced during sustained depolarization was virtually stable, with different oscillation profiles at base and tip. Cyclic movement of the distal region was enhanced at large amplitudes of depolarization. Termination of a hyperpolarizing voltage step induced a transient depolarization-type anterior beating, and termination of a depolarizing step induced a transient posteriad inclination of the transverse cirri. In both hyperpolarizationand depolarization-induced motor responses, a shear angle analysis of the initiation of the response indicated that sliding displacement of doublet microtubules was initiated at the base and propagated towards the tip. The discovery in a ciliary organelle of a very distinct response to hyperpolarizing and depolarizing stimulation is highly useful for the analysis of ciliary electromotor coupling. The functions of intraciliary Ca in the regulation of the motor responses are discussed.