Ion channels and calcium signaling in motile cilia

The beating of motile cilia generates fluid flow over epithelia in brain ventricles, airways, and Fallopian tubes. Here, we patch clamp single motile cilia of mammalian ependymal cells and examine their potential function as a calcium signaling compartment. Resting motile cilia calcium concentration ([Ca²⁺] ~170 nM) is only slightly elevated over cytoplasmic [Ca²⁺] (~100 nM) at steady state. Ca²⁺ changes that arise in the cytoplasm rapidly equilibrate in motile cilia. We measured Ca_V1 voltage-gated calcium channels in ependymal cells, but these channels are not specifically enriched in motile cilia. Membrane depolarization increases ciliary [Ca²⁺], but only marginally alters cilia beating and cilia-driven fluid velocity within short (~1 min) time frames. We conclude that beating of ependymal motile cilia is not tightly regulated by voltage-gated calcium channels, unlike that of well-studied motile cilia and flagella in protists, such as Paramecia and Chlamydomonas.