Voltage-gated Ca2+ channels play a critical role in controlling Ca2+ entry in various cells. Ciliary reversal in Paramecium depends on the Ca2+ influx through voltage-gated Ca2+ channels on the ciliary membrane. One of the voltage-gated Ca2+ channel mutants in Paramecium caudatum. enrC, neither produces Ca2+ action potentials nor responds to any depolarizing stimuli. Here, we report that the enrC(+) acne product is P. caudatum centrin (Pccentrin lp), a member of the Ca2+ -binding EF-hand protein superfamily. The Pccentrin I p gene of cm-C was found to contain a single-base deletion, a mutation that caused the loss of the fourth EF-hand of Pccentrin I p. Moreover, the wild-type Ca2(+) channel function was impaired by Pccentrinlp gene silencing, leading to the loss of current-evoked Ca2+ action potentials and stimulated ciliary reversal. These results demonstrate that Pccentrinlp is indispensable for the activity of the voltage-gated Ca2+ channels that control ciliary reversal in Paramecium. (C) 2004 Elsevier Inc. All rights reserved.