Gravikinesis in Paramecium : theory and isolation of a physiological response to the natural gravity vector

We have investigated a physiological component of the gravitaxis of Paramecium using established mechanisms of ciliate mechanosensitivity. The horizontal, up and down swimming rates of cells, and the sedimentation of immobilized specimens were determined. Weak DC voltage gradients were applied to predetermine the Paramecium swimming direction. An observed steady swimming rate is the vector sum of active propulsion (P), a possible gravity-dependent change in swimming rate ( Delta ), and rate of sedimentation (S). We approximated P from horizontal swimming. S was measured after cell immobilization.