Mechanical and electric correlates of mechanoreceptor activation of the ciliated tail inParamecium

Summary

• 1. Single mechanical pulses were applied by microneedle to the sensitive posterior soma membrane ofParamecium which bears a bundle of immobile and elongated tail cilia. The time sequence of events of stimulation and response was recorded using membrane voltage clamp and microphotography. Deciliation techniques were used to determine the role of cilia in receptor current generation.

• 2. The minimal latency of the receptor current was between 2 and 2.5 ms. Prior to the rise of the current the soma membrane had been deformed in a W-shaped manner, the cell end had widened and shifted anteriorly (Fig. 1).

• 3. With small stimulus amplitudes first signs of the receptor current included an additional delay of about 5 ms. Abrupt transition to the normal response latency occurred upon raising the amplitude of the stimulus.

• 4. The stimulus amplitude determined the rate and amplitude of the receptor current. Decreasing rates of the stimulus increased the response latency.

• 5. The receptor current continued to flow during somatic membrane rebound from indentation. At this time the tail cilia were passively deflected.

• 6. Cell deciliation using 5% ethanol and mechanical agitation did not affect the minimal response latency, but decreased the sensitivity of the tail area. Ethanol-treated ciliated cells were more sensitive than normal cells. These tests suggest that stimulus conduction via the cilia can enhance the receptor response.

• 7. In conclusion, the latency of the receptor current appears to be limited by a transduction mechanism located in the soma. The tail cilia serve to transmit the stimulus including, presumably, spatial and temporal summing of non-local mechanical input.