CHEMOREPELLENTS IN PARAMECIUM AND TETRAHYMENA

Although Paramecium has been widely used as a model sensory cell to st udy the cellular responses to thermal, mechanical and chemoattractant stimuli, little is known about their responses to chemorepellents. We have used a convenient capillary tube repellent bioassay to describe 4 different compounds that are chemorepellents for Paramecium and compa red their response with those of Tetrahymena. The classical Paramecium t-maze chemokinesis test was also used to verify that this is a relia ble chemorepellent assay. The first two compounds, GTP and the oxidant NBT, are known to be depolarizing chemorepellents in Paramecium but t his is the first report of them as repellents in Tetrahymena. The seco nd two compounds, the secretagogue alcian blue and the dye cibacron bl ue, have not previously been described as chemorepellents in either of these ciliates. Two other compounds, the secretagogue AED and the oxi dant cytochrome c, were found to be repellents to Paramecium but not t o Tetrahymena. The repellent nature of each of these compounds is not related to toxicity because cells are completely viable in all of them . More importantly, all of these repellents are effective at micromola r to nanomolar concentrations, providing an opportunity to use them as excitatory ligands in future works concerning their membrane receptor s and possible receptor operated ion channels.