Membrane Control of Ciliary Activity in the Protozoan Euplotes

The locomotory behaviour of ciliated protozoa results from the activity of the cell's cilia. The major variables in the protozoan's ciliary activity are the orientation of the effective stroke and the beating frequency. Ciliary orientation as used here is the direction of ciliary beat, or more specifically, the direction of the effective or power stroke. The effective stroke is defined as that component of ciliary movement which transfers the maximum force to the medium. The effective and recovery phases of the beat can generally be distinguished unequivocally by differences in shape as revealed by visual inspection of high-speed cine pictures. However, the orientation or position in space of the power stroke is more difficult to ascertain and describe. The difficulty lies in documenting with two-dimensional photography the three-dimensional form of the ciliary beat (see Kinosita & Murakami, 1967). The cilia are said to beat in reverse (ciliary reversal) when the power stroke is directed toward the anterior end of the organism so as to propel it backwards (Kinosita & Murakami, 1967).' Normal' beating toward the posterior end causes the organism to swim forward. This will be termed forward beating here. The ability to change ciliary orientation is found in protozoa, the ciliated epithelia of some coelenterates and tunicate larvae. There is evidence that ciliary orientation and frequency of beating are controlled independently. Cilia of Paramecium and Euplotes exposed to 1 mM-NiCl2 stop beating but respond to stimulation by shifting position so as to point toward the anterior end (Naitoh, 1966; Naitoh & Eckert, 1969; Eckert & Naitoh, 1970). Further evidence indicates that Ca is involved in the regulation of ciliary orientation. Ca produces reversal in beating cilia of extracted models of Paramecium in which the cell membrane has been rendered non-selectively permeable with Triton X-100 (Naitoh & Kaneko, 1972). In glycerinated specimens of Paramecium, Naitoh (1969) showed a quantitative relationship between Ca and ciliary orientation in the presence of optimal amounts of ATP, Mg and Zn. Kinosita (1954) found in living Opalina that ciliary reversal in response to stimulation with isotonic-KCl required extracellular Ca. Ciliary orientation varies with membrane potential. Kinosita (1954) found in Opalina that the direction of ciliary beating shifts in a graded manner in response to spontaneous and KCl-evoked changes in membrane potential; others have found ciliary reversal correlated with depolarization, and 'augmentation' (extreme forward