LOW PH LEADS TO SISTER-CHROMATID EXCHANGES AND CHROMOSOMAL-ABERRATIONS, AND ITS CLASTOGENICITY IS S-DEPENDENT

The effect of low pH on sister-chromatid exchanges (SCE), chromosomal aberrations (CA), and the cell cycle were investigated in Chinese hams ter cells. The cells were treated in media over the pH range 7.2-5.4 d uring 24-h continuous or 3-h pulse treatments. In Chinese hamster ovar y K1 cells, slight increases in SCE frequency were induced by 3-h puls e treatment with a 28-h recovery time. In Chinese hamster V79 379A cel ls, similar slight increases in SCE frequency were observed with both treatments. A severe delay in the cell cycle was noted in both cell ty pes. DNA analysis with flow cytometry indicated that the cell cycle de lay occurred in S phase. CA were observed in the first metaphase. Mult iple fixation times over a 27-h period were used to determine whether or not CA could be induced in cells exposed to low pH medium in more t han one part of the cell cycle. Only a few chromatid gaps were induced when the cells were fixed at 0-9 h after the 3-h treatment, most prob ably representing cells that were treated in their G2 or late S phase. CA were induced in cells fixed between 12 and 27 h after the 3-h trea tment. These cells were most probably treated in early S phase, in G1, or in the previous G2/M. These results suggest that low pH clastogeni city is S-dependent.