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

NIH 3T3 fibroblasts expressing the ras oncogene (+ras cells) respond to bradykinin, bombesin or serum with sustained oscillations of cell membrane potential reflecting oscillations of intracellular calcium activity and subsequent activation of calcium-sensitive Kf channels, In contrast, identical cells not expressing the oncogene (-ras cells) respond to bradykinin with a single, transient hyperpolarization of the cell membrane. Furthermore, +ras cells are characterized by a serum-independent proliferation, an increase in cell volume and a marked reorganization of the cytoskeleton, It has been shown previously that the calcium channel blocker nifedipine, but not verapamil and diltiazem, inhibits 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 proliferation, 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) resulted in growth rates which did not differ from untreated +ras cells, The 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 markedly reduced and similar to the values obtained for -ras cells. In addition, bepridil and nifedipine markedly inhibited cytoskeletal rearrangement, i,e. depolymerization of actin-containing stress fibers, This inhibitory effect was not observed for verapamil and diltiazem. The results demonstrate that the inhibition of intracellular calcium activity by bepridil and nifedipine prevents characteristic features of ras oncogene expressing NIH 3T3 fibroblasts such as an increased growth rate and cell volume as well as cytoskeletal rearrangement and oscillations of the cell membrane potential.