Studies on the size, location and turnover of calcium pools accessible to growing Tetrahymena cells.

Tetrahymena pyriformis cells in the logarithmic phase of growth accumulate 2.5--3.75 times as much calcium per unit volume as is present in the growth medium. It appears that most of this calcium is stored in a non-ionic form, with approximately 30% existing in the cilia, near its site of action in effecting ciliary reversal. The exchange of extracellular 45Ca2+ with the major internal pools is extremely rapid, exhibiting a t1/2 of less than 0.5 h. Sites located on the cilia are responsible for 35--50% of Ca2+ influx, with the remainder entering through other positions on the cell surface.