Ca2 +-dependent regulation of beat frequency of cilia in Paramecium

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Abstract
Triton-extracted models of Paramecium cells prepared in the presence of Mg2+ and EGTA showed Ca2+ sensitivity not only in the direction of beat but also in the beat frequency of cilia. The beat frequency increased over a range of concentration of Ca2+ from 2 × 10−7to 4 × 10−7 M, in which the model swam forwards. The frequency increased also above 10−6M-Ca2+, in which the model swam backwards. The increase in frequency was inhibited by calmodulin antagonists. Intracellular injection of a Ca2+ buffer giving a free Ca2+ concentration of 2 × 10−7 to 5 × 10−7M in intact cells induced an increase in the beat frequency. Therefore, it is very likely that the beat frequency of cilia is regulated by the intracellular concentration of Ca2+.