Effects of verapamil on daunomycin cellular retention and cytotoxicity in P388 leukemic cells.

We have utilized digitized video microscopy to investigate the influence of verapamil, a calcium channel blocker, on the in vitro effects of daunomycin in P388 sensitive and resistant sublines. In this study, verapamil enhanced the uptake of daunomycin and its cytotoxicity in both sublines, but the effect was more pronounced in the resistant cells. Flow cytometry showed a pronounced accumulation of resistant cells at G2-M when treated with daunomycin in the presence of verapamil, with no effects observed in the absence of verapamil. Analysis of individual resistant cells using the digitized video fluorescence microscopy technique demonstrated that the influence of verapamil on daunomycin uptake affected all cells and was not restricted to certain subpopulations of cells.