New methods for calculating kinetic properties of cells in vitro using pulse labelling with bromodeoxyuridine

The transit times of Chinese hamster ovary cells through the phases of their cell cycle were measured using dual parameter flow cytometry to measure DNA content and the presence of monoclonal antibodies to bromodeoxyuridine. Up to four separate populations can be accurately measured: unlabelled cells in G2 + M; labelled cells that have not yet divided; labelled cells that have already divided; and the unlabelled cells that were originally in G1 plus the cells that were originally in G2 + M and have since divided. The fractions of cells in these populations can be easily followed in time and the usual kinetic properties can be estimated from these fractions, or combinations thereof, including the times through G1, S, G2 + M and the cycle time. We present equations for analysing this type of data and comment on which equations are most appropriate for measuring specific kinetic properties of the cells.