PHYSIOLOGICAL-PARAMETERS AFFECTING THE CHEMOSENSORY RESPONSE OF TETRAHYMENA

We have investigated the significance of a number of physiological par ameters in the preparation of cells for experiments on chemokinesis in Tetrahymena. The study comprises (1) growth state of the cells, (2) c omposition of the starvation medium, (3) concentration of cells during starvation, (4) oxygen saturation of the starvation medium, (5) tempe rature during starvation, and (6) starvation period. By controlling th e physiological state of the cells, we significantly improved the repr oducibility of the results obtained in assays for chemokinesis in Tetr ahymena. In short, cells optimal for chemokinesis at an assay temperat ure of 28 degrees C should be starved from the exponential growth phas e in a concentration below 2 X 10(5) cells ml(-1) for 10-20 h. The sur face-to-volume ratio of the starvation medium-water or Hepes buffer-sh ould be about 5 cm(-1) (or more) to ensure more than 95% oxygen satura tion of the starvation medium. Maximal chemosensory responses were obt ained if the cells were starved at 21 degrees C. The chemokinetic pote ntial of the cells decreased significantly, as did the levels of the r atio of ATP to ADP, if cells were starved at higher temperatures. A te ntative correlation between the ATP level in the cells and the chemose nsory potential of the cells has been found. We suggest that chemokine sis is a constant quality of Tetrahymena, because we found no sign tha t 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 chemoat tractants.