Paramecium cells swim by beating their cilia, and make turns by transiently reversing their power stroke. Reversal is caused by Ca2+ entering the cilium through voltage-gated Ca2+ (CaV) channels that are found exclusively in the cilia. As ciliary Ca2+ levels return to normal, the cell pivots and swims forward in a new direction. Thus, the activation of the CaV channels causes cells to make a turn in their swimming paths. For 45 years, the physiological characteristics of the Paramecium ciliary CaV channels have been known, but the proteins were not identified until recently, when the P. tetraurelia ciliary membrane proteome was determined. Three CaVα1 subunits that were identified among the proteins were cloned and confirmed to be expressed in the cilia. We demonstrate using RNA interference that these channels function as the ciliary CaV channels that are responsible for the reversal of ciliary beating. Furthermore, we show that Pawn (pw) mutants of Paramecium that cannot swim backward for lack of CaV channel activity do not express any of the three CaV1 channels in their ciliary membrane, until they are rescued from the mutant phenotype by expression of the wild-type PW gene. These results reinforce the correlation of the three CaV channels with backward swimming through ciliary reversal. The PwB protein, found in endoplasmic reticulum fractions, co-immunoprecipitates with the CaV1c channel and perhaps functions in trafficking. The PwA protein does not appear to have an interaction with the channel proteins but affects their appearance in the cilia.
The authors declare no competing or financial interests.
S.L., J.Y. and J.L.V.H. designed and conducted the study. S.L. and J.Y. carried out all laboratory work and performed data analysis. J.L.V.H. and M.S.V. wrote the manuscript with contributions from J.Y.
Research reported in this publication was supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences (NIGMS) of the National Institutes of Health (NIH) under grant number P20GM103449 to J.L.V.H. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of NIGMS or NIH. Deposited in PMC for release after 12 months.
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.141234.supplemental
- Received March 31, 2016.
- Accepted July 19, 2016.
- © 2016. Published by The Company of Biologists Ltd