Two mechanisms of chemotaxis inParamecium

Summary Paramecia show chemotaxis, that is, they accumulate in or disperse from the vicinity of chemicals. This study examines both the avoiding reactions (abrupt random changes of swimming direction) and velocities of normal and mutant paramecia in attractants and repellents and shows that the animals accumulate or disperse either by changing the frequency of avoiding reactions or by changing swimming velocity. Mutations or conditions that eliminate avoiding reactions abolish the chemotaxis response to chemicals that cause accumulation or dispersal by modulation of frequency of avoiding reactions but not the response to chemicals that cause chemotaxis by modulation of velocity.The current knowledge of the bioelectric control of the swimming behavior inParamecium and observations of mutants defective in bioelectric control and in chemotaxis are used to develop a hypothesis for membrane potential control of chemotaxis: attractants that require the avoiding reaction slightly hyperpolarize the membrane; repellents that require the avoiding reaction slightly depolarize the membrane; repellents that cause chemitaxis by modulation of velocity strongly hyperpolarize the membrane.I am grateful to D. Kusher and P. Foletta for their technical assistance, to C. Kung and E. Orias for support and discussion of this work, to H. Machemer and M. Levandowsky for stimulating discussions, and to B. Diehn for suggestion of the modified assay. This work was supported in part by Public Health Service Grant F32 NSO5587 to JVH and NSF GB-3164X and PHS GM-19406 to C. Kung.