Calmodulin and Ca2+/calmodulin-binding proteins are involved in Tetrahymena thermophila phagocytosis

The ciliated protist, Tetrahymena thermophila, possesses one oral apparatus for phagocytosis, one of the most important cell functions, in the anterio r cell cortex. The apparatus comprises four membrane structures which consi st of ciliated and unciliated basal bodies, a cytostome where food is colle cted by oral ciliary motility, and a cytopharynx where food vacuoles are fo rmed. The food vacuole is thought to be transported into the cytoplasm by a deep fiber which connects with the oral apparatus. Although a large number of studies have been done on the structure of the oral apparatus, the mole cular mechanisms of phagocytosis in Tetrahymena thermophila are not well un derstood. In this study, using indirect immunofluorescence, we demonstrated that the deep fiber consisted of actin, CaM, and Ca2+/CaM-binding proteins , p85 and EF-1 alpha, which are closely involved in cytokinesis. Moreover, we showed that CaM, p85, and EF-1 alpha are colocalized in the cytostome an d the cytopharynx of the oral apparatus. Next, me examined whether Ca2+/CaM signal regulates Tetrahymena thermophila phagocytosis, using Ca2+/CaM inhi bitors chlorpromazine, trifluoperazine, N-(6-aminohexyl)-1-naphthalenesulfo namide, and N-(6-aminohexyl)-5-chloro-1-naphthalene HCl. In Tetrahymena, it is known that Ca2+/CaM signal is closely involved in ciliary motility and cytokinesis. The results showed that one of the inhibitors, N-(6-aminohexyl )-5-chloro-1-naphthalenesulfonamide HCl, inhibited the food vacuole formati on rather than the ciliary motility, while the other three inhibitors effec tively prevented the ciliary motility. Considering the colocalization of Ca M, p85, and EF-1 alpha to the cytopharynx, these results suggest that the C a2+/CaM signal plays a pivotal role in Tetrahymena thermophila food vacuole formation.