EFFECTS OF CALCIUM-CHANNEL BLOCKERS ON NIH 3T3 FIBROBLASTS EXPRESSINGTHE HA-RAS ONCOGENE

NIH 3T3 fibroblasts expressing the ras oncogene (+ras cells) respond t o bradykinin, bombesin or serum with sustained oscillations of cell me mbrane potential reflecting oscillations of intracellular calcium acti vity and subsequent activation of calcium-sensitive Kf channels, In co ntrast, identical cells not expressing the oncogene (-ras cells) respo nd to bradykinin with a single, transient hyperpolarization of the cel l membrane. Furthermore, +ras cells are characterized by a serum-indep endent proliferation, an increase in cell volume and a marked reorgani zation of the cytoskeleton, It has been shown previously that the calc ium channel blocker nifedipine, but not verapamil and diltiazem, inhib its oscillations of cell membrane potential as well as proliferation, In this study, we have examined the effect of several calcium channel blockers (bepridil, nifedipine, verapamil, diltiazem) on the prolifera tion, volume and cytoskeletal reorganization of +ras cells, Bepridil ( 10 mu mol/l), which is also shown here to inhibit oscillations of cell membrane potential, and nifedipine (10 mu mol/l) caused a decrease in cell number, whereas verapamil and diltiazem (10 mu mol/l each) resul ted in growth rates which did not differ from untreated +ras cells, Th e increase in cell volume as observed in untreated +ras cells was also observed for cells treated with verapamil and diltiazem, whereas cell volumes of +ras cells treated with bepridil and nifedipine were marke dly reduced and similar to the values obtained for -ras cells. In addi tion, bepridil and nifedipine markedly inhibited cytoskeletal rearrang ement, i,e. depolymerization of actin-containing stress fibers, This i nhibitory effect was not observed for verapamil and diltiazem. The res ults demonstrate that the inhibition of intracellular calcium activity by bepridil and nifedipine prevents characteristic features of ras on cogene expressing NIH 3T3 fibroblasts such as an increased growth rate and cell volume as well as cytoskeletal rearrangement and oscillation s of the cell membrane potential.