THE CONCEPTS OF TAIL MOMENT AND TAIL INERTIA IN THE SINGLE-CELL GEL-ELECTROPHORESIS ASSAY

Single cell gel electrophoresis under alkaline conditions is a techniq ue used to detect primary DNA damage in individual mammalian cells. Ce lls embedded in agarose on microscope slides are subjected to lysis, u nwinding of DNA and electrophoresis at high pH. After staining with a fluorescent dye, cells with DNA damage display increased migration of genetic material from the cell nucleus. The damage is quantified by me asuring the displacement between the genetic material of the nucleus ( 'comet head') and the resulting 'tail'. The torsional moment of the ta il ('tail moment') has been suggested to be an appropriate index of in duced DNA damage in considering both the migration of the genetic mate rial as well as the relative amount of DNA in the tail. In the present paper it will be shown that the moment of inertia ('tail inertia'), a not previously described tail parameter, provides a more precise desc ription of the distribution of individual DNA fragments within the tai ls. The tail inertia was also found to be the most sensitive indicator of the DNA damage induced in peripheral lymphocytes from mice given a single intraperitoneal injection of cyclophosphamide (150 mg/kg b.w.) . It is concluded that the tail inertia is an important complement to other tail parameters when looking for damage of DNA with the single c ell gel electrophoresis assay.