Centrin is essential for the activity of the ciliary reversal-coupled voltage-gated Ca ²⁺ channels

Voltage-gated Ca ²⁺ channels play a critical role in controlling Ca ²⁺ entry in various cells. Ciliary reversal in Paramecium depends on the Ca ²⁺ influx through voltage-gated Ca ²⁺ channels on the ciliary membrane. One of the voltage-gated Ca ²⁺ channel mutants in Paramecium caudatum, cnrC, neither produces Ca ²⁺ action potentials nor responds to any depolarizing stimuli. Here, we report that the cnrC ⁺ gene product is P. caudatum centrin (Pccentrin1p), a member of the Ca ²⁺-binding EF-hand protein superfamily. The Pccentrin1p gene of cnrC was found to contain a single-base deletion, a mutation that caused the loss of the fourth EF-hand of Pccentrin1p. Moreover, the wild-type Ca ²⁺ channel function was impaired by Pccentrin1p gene silencing, leading to the loss of current-evoked Ca ²⁺ action potentials and stimulated ciliary reversal. These results demonstrate that Pccentrin1p is indispensable for the activity of the voltage-gated Ca ²⁺ channels that control ciliary reversal in Paramecium.