RADIATION-INDUCED CELL-KILLING IS HIGHLY DEPENDENT UPON BUFFER TREATMENT (FILTRATION COMPARED TO AUTOCLAVING) DUE TO METAL-CATALYZED FORMATION OF HYPOCHLORITE - A CAUTIONARY NOTE

Buffer solutions used in experiments in radiation biology may be steri lized by either autoclaving or filtration. We show here that for phosp hate-buffered saline such differences in buffer treatment may result i n widely differing dose-effect curves for cell killing. The temperatur e-dependent transformation of monophosphate ions into di- or polyphosp hate evidently proceeds to an appreciable extent upon autoclaving the buffers at 120 degrees C for 10 to 20 min. This increases the capabili ty of the buffer to chelate spurious metal contaminations and, as a co nsequence, to reduce the amount of cytotoxic hypochlorite being produc ed. Depending on conditions of buffer treatment we have observed dose modification factors for the colony-forming ability of yeast cells up to the order of 3. Thus effects due to buffer treatment might easily o utweigh the effect which the experiment was originally designed to det ermine. We strongly advise, therefore, hat results of parallel sets of experiments in which different methods of buffer sterilization have b een used should not be compared directly. (C) 1996 by Radiation Resear ch Society.