Artificial deciliation causes loss of calcium-dependent responses in Paramecium

Abstract

WHEN a paramecium collides with an obstacle, it reverses the direction of the effective stroke of its cilia, swims backwards for a while, and, with one or more repetitions of this ‘ciliary reversal’ response, avoids the obstacle1. When the medium is disturbed2 or when the posterior part of its body is stimulated mechanically, it swims faster than usual and escapes from the stimulus mainly by increasing the frequency of ciliary beat. The current view of the underlying mechanisms can be summarised as follows3,4. A mechanical stimulus to the anterior end of the animal deforms the cell membrane of this region, increasing the permeability to Ca2+ and causing a depolarisation which further activates the Ca2+-channels in the membrane. Thus, the depolarisation develops regeneratively towards the equilibrium potential of Ca2+. The Ca2+ which has entered the cell acts on some mechanism controlling the direction of ciliary beat to bring about ciliary reversal. On the other hand, a stimulus to the posterior end activates the K+-channels in the membrane, causing hyperpolarisation and an increase in ciliary beat frequency. Although the animal behaves as a mechanoreceptor cell in the early stages of these events, it is not clear which part of the cell transduces the mechanical stimulus to the activation of Ca2+- or K+-channels. We report here the effect of removal of cilia on the electro-physiological responses of paramecium to mechanical as well as some other stimuli.