SINGLE-CELL GEL TECHNIQUE SUPPORTS HIT PROBABILITY-CALCULATIONS

We have used the alkaline single-cell gel technique to provide a biolo gical estimate of the percentage of cell nuclei ''hit'' by alpha parti cles during in vitro radon exposure. The single-cell gel electrophoret ic technique measures DNA strand breaks as increased migration of the DNA out of lysed cells embedded in the middle layer of a three-layer g el formed on a microscope slide. Two of the advantages of this system are that individual cells of an exposed population can be evaluated an d that histograms can be constructed to estimate the population respon se. Chinese hamster ovary and A(L) cells were each exposed to 0.39 Gy of radon, a dose at which our dosimetry model predicts that 63 and 73% , respectively, of the cell nuclei will be traversed by an alpha parti cle. The difference in the percentages at similar doses is mainly due to the larger nucleus volume in A(L) cells. A 1.5-Gy x-ray response wa s also evaluated as a low-LET control. As expected, the x-ray profile of DNA damage was shifted from the nonirradiated profile in the direct ion of greater DNA migration and approximated a normal distribution. T he profile of the radon-exposed cells was biphasic, with one distribut ion corresponding to the control (nonirradiated) response and the othe r profile showing increased DNA migration. We interpret the second pro file in the biphasic profile as representing cell nuclei that had rece ived an alpha ''hit.'' The percentages of cell nuclei in the ''hit'' c ategory (approximately 51 and 45% for CHO and A(L), respectively), as judged by the single-cell gel technique, were 81 and 62% of the calcul ated values.