Biochemical Studies on Irradiated Protozoa. I. Effect of Metabolites on the Respiration of X‐Irradiated Tetrahymena pyriformis*

Abstract

SYNOPSIS. When Tetrahymena suspended in water were given increasing doses of radiation, oxygen consumption decreased with increasing dose, reaching 60–90% at 600,000 r. Cells irradiated in 0.07 M phosphate buffer, pH 7.4, showed no significant decrease in oxygen consumption even at 600,000 r. The decrease in respiration observed on irradiation of Tetrahymena pyriformis W in water with 300,000 r of X‐radiation was prevented by addition of pyruvate or acetate during or immediately after irradiation. Pyruvate stimulated the respiration of the X‐irradiated cells, particularly at 10 and 60 min post‐irradiation. Lactate markedly stimulated the respiration of control suspensions of Tetrahymena cells and oxidation of lactate by cells irradiated with 300,000 r was increased by 20 to 100%, depending on the concentration of lactate and the time after irradiation. Pyruvate was considerably more effective than lactate in increasing O2 uptake of X‐irradiated cells, particularly at 10 min post‐irradiation. Thioctic acid affected neither the respiration of control or X‐irradiated Tetrahymena nor the oxidation of pyruvate. The growth lag of Tetrahymena increased proportionately with increasing radiation dose; no cells survived 600,000 r. The presence of metabolites during irradiation did not affect the lag period or subsequent growth rates. The effects observed were discussed in terms of an alteration of the permeability of Tetrahymena after irradiation.