is a small protozoan cell, which has less than 10 % of the volume
of the well-known Parameciumcaudatum. We investigated the graviresponses of Tetrahymena in a search of the lower limits of gravitransduction
in ciliates. Equilibrated populations of free swimming cells were
enclosed in chambers of 2 mm depth testing the orientational and
speed responses with the chambers in horizontal or vertical position.
For determinations of gravikinesis, the sedimentation rates of cells
immobilized by application of two different procedures were measured.
Negative gravitaxis was pronounced after turning the chambers from
horizontal to vertical position; it settled, after 1 min, toward
an orientation coefficient of 0,2. Gravikinesis did not only neutralize
the sedimentation rate (= 22 µm s–1) but even exceeded that rate by at least 30 %. Tetrahymena is thereby the
first cell, in which overcompensation of the sedimentation rate
was documented. Biophysical considerations suggest a high gravisensitivity
with channel gating energy being less than 33 times above the thermic