A Comparison of the Polycation Receptors of Paramecium tetraurelia and Tetrahymena thermophila

Chemorepellents are compounds that cause ciliated protozoans to reorient their swimming direction. A number of chemorepellents have been studied in the ciliated protozoans, Paramecium and Tetrahymena. Chemorepellents, such as polycations, cause the organism to exhibit "avoidance behavior," a swimming behavior characterized by jerky movements and other deviations from normal forward swimming, which result from ciliary reversal. One well-characterized chemorepellent pathway in Tetrahymena is that of the proposed polycation receptor that is activated by lysozyme and pituitary adenylate cyclase activating polypeptide (PACAP). In this study, we compare the response of Paramecium to the chemorepellents lysozyme, vasoactive intestinal peptide (VIP), and PACAP to the previously studied polycation response in Tetrahymena. Our results indicate that lysozyme, VIP, and PACAP are all chemorepellents in Paramecium, just as they are in Tetrahymena. However, the signaling pathways involved appear to be different. While previous pharmacological characterization indicates that G-proteins are involved in polycation signaling in Tetrahymena, we present evidence that similar reception in Paramecium involves activation of a tyrosine kinase pathway in order for lysozyme avoidance to occur. Polycation responses of both organisms are inhibited by neomycin sulfate. While PACAP is the most effective of the three chemorepellents in Tetrahymena, lysozyme is the most effective chemorepellent in Paramecium.