An ATP Receptor in Tetrahymena
Todd Hennessey Principal Investigator
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ATP is an excitatory neurotransmitter in most multicellular organisms. However, preliminary evidence suggests that ATP receptors are found even in unicellular organisms, specifically in the ciliate Tetrahymena. This evidence suggests that the Tetrahymena receptor serves as a chemorepellent receptor by eliciting an ATP-dependent membrane depolarization (by inducing a change in membrane calcium conductance) and action potentials that result in repetitive bouts of backward and forward swimming called "avoiding reactions". This behavior re-orients the cells to enable them to avoid high concentrations of ATP, a compound normally released by lysed cells. This is similar to the proposed role of external ATP as an indicator of cell lysis in pain reception in vertebrates. Thus, ATP reception in Tetrahymena may be an evolutionary precursor to neurotransmission in higher organisms, and the Tetrahymena ATP receptor may have significant similarities to vertebrate ATP receptors. Such a similarity is further suggested by the ability of an antibody made against a subset of vertebrate ATP receptors (P2X1 receptors) to cross-react with a membrane protein of Tetrahymena. Experiments will determine if this protein is the ATP receptor and, if so, to characterize it. Immunoprecipitation will be used as a basis for purification. Behavioral bioassays, and electrophysiological, molecular biological and biochemical techniques will be utilized to verify the location of the receptor in the cell and to determine its properties. Additional studies will determine of the biochemical mechanisms involved in chemosensory adaptation. This work will advance basic knowledge of chemorepellent reception and adaptation, and will provide insights into the evolution of neurotransmitter systems. The project will also contribute towards education of students at the high school, undergraduate and graduate levels who will participate in the research.