The inward calcium current is increased by sterol supplementation in Paramecium

1. 1. The amplitude of the isolated voltage dependent inward calcium current of axenically grown Paramecium was greater in cells grown with sitosterol than those grown in stigmasterol supplemented medium. 2. 2. The duration of high K⁺ stimulated backward swimming, a bioassay for estimating calcium channel activity, was also increased in sitosterol supplemented cells. 3. 3. The major difference in the ciliary membrane lipids of cells grown in sitosterol medium was in the type and not the amount of sterols present. Other small differences were also noted in the phospholipids and fatty acids of sitosterol supplemented ciliary membranes. 4. 4. This work suggests that the type of dietary sterol can affect the excitability of cells by affecting the amplitude of the inward calcium current. The possible mechanisms involved in these effects are discussed.