INHIBITION OF PDGF-MEDIATED PROLIFERATION OF VASCULAR SMOOTH-MUSCLE CELLS BY CALCIUM-ANTAGONISTS

Background and Purpose The mechanism by which calcium antagonists (CAs ) inhibit proliferation in vascular smooth muscle cells (VSMCs) is not yet fully understood. We investigated the effects of four CAs (clenti azem, verapamil, diltiazem, and nifedipine) on signal transduction pat hways activated by platelet-derived growth factor (PDGF). To determine these effects, the levels of inositol phosphates (IPs). protein kinas e C (PKC), and the induction of the transcription factor activator pro tein-1 (AP-I) were measured. Methods The mitogenic effect of PDGF on V SMCs was measured by [H-3]thymidine incorporated into DNA. IP producti on was monitored by [H-3]myo-inositol incorporation. PKC activation wa s determined by measurement of myristoylated, alanine-rich C kinase su bstrate (MARCKS) phosphorylation in digitonin-permeabilized VSMCs. The induction of AP-1 complex was detected by electrophoretic mobility sh ift assays. Results Each CA significantly inhibited the [H-3]thymidine incorporation into DNA in unstimulated cells. Similar significant dec reases in [H-3]thymidine incorporation by CAs were observed when cells were stimulated by rPDGF-BB. The phosphorylation of MARCKS mediated b y rPDGF-BB was significantly reduced by each CA. Clentiazem and verapa mil significantly reduced the expression of AF-I induced by rPDGF-BB ( P<.01, P<.05). Clentiazem also significantly reduced the expression of AP-1 induced by rPDGF-AB (P<.05). Conclusions PDGF-mediated prolifera tion of VSMCs correlates with activation of PKC but nor with induction of the AP-1 complexes. In addition, our results suggest that CAs bloc k proliferation of VSMCs by inhibiting DNA synthesis, possibly via PKC .