Receptor current following controlled stimulation of immobile tail cilia inParamecium caudatum

Summary

• 1. Directionally and amplitude-controlled mechanical pulses were applied to identified sites of the tail cilia and the posterior soma membrane ofParamecium under voltage clamp.

• 2. Lateral stimuli directed toward more distal sections of the cilia deflected the ciliary bundle as a unit. No deformations of the soma membrane were detected upon stimulus application to the ciliary shafts (Fig. 3).

• 3. Outward receptor currents following somatic stimulation arose 3 ms after the onset of the electric driving pulse (= response time). The response times after ciliary stimulation were at least 6 ms.

• 4. The response times rose from 6 to beyond 10 ms after shifts of the stimulus probe from proximal to more distal sections of the tail cilia.

• 5. Maximal currents (up to 17 nA) were recorded upon stimulation of the apical posterior soma in the center of the tail. Ciliary stimulation elicited currents which had more irregular time courses of rise and decay.

• 6. In most cells tested the current amplitudes were reduced with shifts from somatic to ciliary stimulation; the amplitudes even more decreased with stimulus displacement toward the ciliary tips. A fraction of cells was hypersensitive in that the responses to somatic and ciliary stimulation were enhanced as compared to normal cells.

• 7. The tail cilia showed no intrinsic directional sensitivity. Minor differences in responsiveness to topographically identified lateral stimulation of the cilia are presumably related to a dorso-ventral differentiation of somatic sensitivity.

• 8. We conclude that neither the ciliary membrane nor the axoneme and basal body play an active role in mechanotransduction. A local ciliary stimulus appears to be ‘defocused’ so that it affects an extended area of the sensitive soma membrane.