Microtubule-stabilizer epothilone B counteracts anesthetic-induced slowed swimming in Tetrahymena pyriformis

Volatile anesthetics that reversibly render humans immobile and unconscious have analogous reversible effects on the motility of non-neural organisms including plants and single cells. The molecular mechanisms by which they do this remain unclear, but are difficult to study in mammals because of complex interactions among diverse tissues and cell types. Here we use freely available software to study cell swimming speeds in the single-celled ciliate species Tetrahymena pyriformis. We first extend previous findings with other volatile anesthetics, to show that isoflurane also reversibly slows swimming speed in Tetrahymena. We then show that prior exposure to the microtubule (MT) stabilizing drug epothilone B (10 nM) confers resistance to isoflurane's anesthetic effect on swimming speed. This result suggests that isoflurane slows swimming in part by interacting with MTs. This conclusion is consistent with our previous experiments supporting that binding to MTs contributes to isoflurane-induced unconsciousness in rats and mice. Our present results are thus consistent with the hypothesis that all ciliates are sensitive to volatile anesthetics, and support conserved molecular mechanisms of anesthetic action in single-celled organisms and mammals. Moreover, our preparation enables inexpensive high-throughput testing of the functional roles played by specific candidate molecular targets of volatile anesthetics in ciliates.