Increase of intracellular pH in p53-dependent apoptosis of thymocytes induced by gamma radiation.

ABSTRACT

Irradiation with gamma rays induces apoptosis of thymocytes by a p53-dependent pathway, but its mechanism is not clear. In this study, we report that gamma-ray-induced apoptosis was associated with the intracellular alkalinization of the thymocytes. After exposure to gamma rays, thymocytes underwent apoptosis when cultured in vitro, and the degree of apoptosis was dependent on the incubation period The longer the incubation period, the greater the number of cells undergoing apoptosis. However, this apoptosis could be inhibited by the acidic condition of the culture. There was a positive correlation between the pHi of thymocytes and the degree of apoptosis. Treatment with gamma radiation induced apoptosis as well as the elevation of the pHi in thymocytes. The intracellular pH was higher in pre-apoptotic thymocytes than in those that did not undergo apoptosis. Furthermore, apoptosis induced by gamma radiation was inhibited by cycloheximide, actinomycin D or the intracellular Ca2+ chelator, TMB-8. The p53 protein is induced after gamma irradiation. Thus it appears that intracellular pH is increased during the gamma-ray-induced p53-dependent apoptosis of thymocytes.