A radioisotopic and morphological study of the uptake of materials into food vacuoles byTetrahymena pyriformis GL-9

Summary

A study has been made of the endocytic uptake of H³- or C¹⁴-sucrose, I¹²⁵-albumin and P¹²⁵-polyvinylpyrrolidone (P.V.P.) by starvedTetrahymena pyriformis GL-9. It has been shown that the concentration of these materials in digestive vacuoles was normally increased by a factor of 20–50 fold as compared to the extracellular medium. The average number of molecules of albumin which must be adsorbed before the cell was induced to form a digestive vacuole was about 4×10⁷ molecules. In conditions of “excess” albumin the cell could adsorb about four times this amount in each digestive vacuole. The minimum concentration of adsorbed albumin molecules needed to induce formation of a digestive vacuole was about 1×10⁶ per μm² of vacuolar membrane. Sucrose, whilst being concentrated in vacuole formation induced by the presence of albumin, would not itself induce any vacuole formation. The number of molecules adsorbed per digestive vacuole appeared to be directly related to the extracellular concentration of sucrose over the range studied. This enhanced incorporation of sucrose into digestive vacuoles was not due to adsorption on to the albumin molecules, with subsequent normal vacuole formation. It was also not accounted for by any active transport mechanism and thus appeared to be a true endocytic uptake.

The effect of addition of cytochalasin B was to markedly inhibit vacuole formation; but the incorporation of radioisotopes was not reduced to the extent thought to be likely from calculations of the decrease in cellular vacuole concentration. This discrepancy could have been due either to micropinocytosis or to an increased level of adsorption into the few vacuoles formed in the cytochalasin B inhibited cells. The results are discussed.