Divalent cations and inorganic phosphate metabolism in starved Tetrahymena

Tetrahymena pyriformis maintained under starvation conditions release orthophosphate into the suspension medium. Ca²⁺ and/or Mg²⁺ addition reduced the amount of orthophosphate excreted during a 3-h period. Cellular orthophosphate levels were not altered by divalent cation supplements; however, an increase in the pyrophosphate content was observed which was equivalent in amount to the reduction in orthophosphate efflux. These observations suggest that divalent cations are important not only in the acquisition of phosphorus during growth but also in the conservation of this element during starvation.