ION REGULATION IN TETRAHYMENA

¹ Department of Zoology, University of Chicago, Chicago 37, Ill.

1. The K and Na content of Tetrahymena pyriformis has been determined, and the mechanisms of ionic regulation were investigated.

2. The main findings were: K and a small amount of Na are maintained in very dilute medium. Cellular K and Na are readily exchangeable with K and Na of the medium. However, small, constant amounts of each are unexchangeable. Cells rapidly equilibrate with media high in K or Na. High K washes out of cells slowly, whereas Na enters and washes out of cells with equal facility. There is no reciprocal relationship between cellular K and Na. Tetrahymena contains little Cl. Increases in cellular K or Na are not accompanied by increases in Cl.

3. The results are interpretable according to the following proposals: K is specifically accumulated and retained by a system of internal binding sites with a saturation level. Na is probably retained by a separate mechanism. There is also a Na extrusion mechanism which has no relationship with K or Na retention. Cellular K and Na are compartmentalized into three components: unexchangeable, exchangeable but bound, and freely diffusible components.