Frequency and directional responses of cilia to membrane potential changes inParamecium

Abstract

Ciliary motor reactions and membrane responses to injected current stimulation inParamecium caudatum were recorded with a combined electrophysiological and high-speed cine system to investigate relations between ciliary activity and membrane potential. The power stroke of the cilia normally directed to the right rear rotates clockwise to a more posterior orientation in response to hyperpolarizing stimulation. Depolarization induces a counterclockwise shift, usually leading to the rapid reversal of beat direction toward the anterior end (Fig. 15). Ciliary frequency is increased either with hyperpolarization or with moderate or strong depolarization of the cell membrane. The frequency response is linked to the directional response in such a way that minimal frequency occurs during transition from reversed to normal beating, and that with increasing clock-wise or counterclockwise angular deviation of the power stroke from this sector of transition the frequency of beat is increased. In the course of transition from the reversed to normal beating the cilia are inactivated, i.e. they stick out perpendicularly to the cell surface without a polarized beat. A depression in normal beating activity somewhat resembling inactivation occurs with small depolarizations. Hyperpolarization-induced frequency time courses are significantly slower than those evoked by membrane depolarization. The role of transmembrane calcium fluxes and consequent modification of intraciliary calcium concentrations is considered with regard to the observed ciliary responses.