PHYSIOLOGICAL-PARAMETERS AFFECTING THE CHEMOSENSORY RESPONSE OF TETRAHYMENA

We have investigated the significance of a number of physiological parameters in the preparation of cells for experiments on chemokinesis in Tetrahymena. The study comprises (1) growth state of the cells, (2) composition of the starvation medium, (3) concentration of cells during starvation, (4) oxygen saturation of the starvation medium, (5) temperature during starvation, and (6) starvation period. By controlling the physiological state of the cells, we significantly improved the reproducibility of the results obtained in assays for chemokinesis in Tetrahymena. In short, cells optimal for chemokinesis at an assay temperature of 28 degrees C should be starved from the exponential growth phase in a concentration below 2 X 10(5) cells ml(-1) for 10-20 h. The surface-to-volume ratio of the starvation medium-water or Hepes buffer-should be about 5 cm(-1) (or more) to ensure more than 95% oxygen saturation of the starvation medium. Maximal chemosensory responses were obtained if the cells were starved at 21 degrees C. The chemokinetic potential of the cells decreased significantly, as did the levels of the ratio of ATP to ADP, if cells were starved at higher temperatures. A tentative correlation between the ATP level in the cells and the chemosensory potential of the cells has been found. We suggest that chemokinesis is a constant quality of Tetrahymena, because we found no sign that prolonged starvation or other changes applied to the cells produced an up-regulation of the chemosensory response. Apparently, starvation is obligatory only to remove the growth medium (which is itself a very potent attractant), thereby making the cells sensitive to the chemoattractants.