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.
2. An observed steady swimming rate is the vector sum of active propulsion (P), a possible gravity-dependent change in swimming rate (D), and rate of sedimentation (S). We approximated P from horizontal swimming. S was measured after cell immobilization.
3. Theory predicts that the difference
between the down and up swimming rates, divided by two, equals the
sum of S and J. J is supposed to be the arithmetic mean of two subcomponents,
gravistimulation of the anterior and posterior cell ends, respectively.