Ionic conductances of membranes in ciliated and deciliated Paramecium.

Abstract

P. caudatum was deciliated with ethanol. The ionic conductance of the membrane was investigated with constant current, voltage clamp and mechanical stimuli. The resting potential was not modified by the removal of the cilia. The dependence of the resting potential on the extracellular concentrations of Ca and K was the same in deciliated and control cells. The input resistance in deciliated and ciliated cells increased after ethanol treatment. The membrane capacitance decreased to 48% after deciliation, suggesting that the ciliary surface area is equal to the somatic surface area. Deciliation completely removed the regenerative response (graded action potential) elicited by depolarizing current pulses or mechanical stimuli. Deciliated cells retained the depolarizing and hyperpolarizing mechanoreceptor responses. Voltage-clamp experiments demonstrated the loss of the early inward current in deciliated cells; it was restored during ciliary regeneration. Steady-state current-voltage relationships were unchanged by deciliation. The time courses of the recovery of the membrane capacitance and of the early inward current were similar, suggesting that the number of voltage-sensitive Ca channels is proportional to the ciliary membrane area. The voltage-sensitive Ca channels reside in the ciliary membrane (in confirmation of Dunlap, 1976; Ogura et Takahashi, 1976), while mechanoreceptor channels, rectifier channels and resting conductances are localized in the somatic membrane.