VERAPAMIL INHIBITS PROLIFERATION, MIGRATION AND PROTEIN-KINASE-C ACTIVITY IN HUMAN RETINAL-PIGMENT EPITHELIAL-CELLS

The effects of three calcium channel blockers, verapamil, diltiazem an d nifedipine, were examined on in vitro proliferation and migration of human retinal pigment epithelial cells. Human retinal pigment epithel ial cells were seeded in Dulbecco's modified essential medium with 10% fetal bovine serum and different concentrations of the three calcium channel blockers. After 3 days of treatment, cell proliferation was de termined by cell counting and by [H-3]-thymidine uptake. Cell viabilit y was determined with trypan blue exclusion. For determination of cell migration, retinal pigment epithelial cells were grown to confluence and then growth-inhibited with mitomycin C. After a 3 mm zone was denu ded, the cells were treated with different concentrations of the calci um channel antagonists. After 24 hr, the cells that had migrated over the wound edge were counted. To determine the involvement of protein k inase C in the verapamil effect, its activity was measured in both ver apamil-treated and untreated cells. Verapamil dose dependently inhibit ed serum-induced proliferation of retinal pigment epithelial cells, wh en measured by cell number (IC50 14.6 mu M) or [H-3]-thymidine incorpo ration (IC50 11.3 mu M). At concentrations of 15 mu M and below, there was no effect on cell viability, as determined by morphology and tryp an blue exclusion. Diltiazem inhibited cell proliferation at a concent ration of 100 mu M; however, 100 mu M nifedipine had no effect. Verapa mil showed a significant inhibition of serum-induced migration in the range of 10 mu M to 0.1 mu M. The IC50 of the inhibition of retinal pi gment epithelial cell proliferation and migration by verapamil is sign ificantly higher than that seen for effects on calcium channel blockag e. Eight micromolar verapamil reversibly inhibited total protein kinas e-C activity in retinal pigment epithelial cells suggesting the possib ility that the drug may act by inhibiting the protein kinase-C pathway . These data suggest the potential of the calcium channel blocker vera pamil as a pharmacological modulator of disorders such as proliferativ e vitreoretinopathy in which there is increased retinal pigment epithe lial cell proliferation and migration. (C) 1998 Academic Press.