Differential effects of lovastatin on mitogen induced calcium influx in human cultured vascular smooth muscle cells

1 In this study the effect of lovastatin, an inhibitor of cholesterol and isoprenoid synthesis, on the rises in intracellular calcium concentration ([Ca2+](i)) induced by platelet derived growth factor BB (PDGF-BB), angiotensin II (AII), low density lipoproteins (LDL) and foetal calf serum (FCS) was examined in human cultured vascular smooth muscle cells (VSMC) from saphenous vein. Changes in [Ca2+](i) were measured in cell suspensions by the Ca2+ sensitive probe, fura 2. 2 Incubation with lovastatin for 24-26 h markedly reduced the peak rise and sustained phase of [Ca2+](i) elevation in response to PDGF-BB but the responses to AII, LDL and FCS were unaffected. Further experiments showed that lovastatin pretreatment inhibited PDGF-BB induced Ca2+ influx but not intracellular Ca2+ release. This inhibition could be overcome by co-incubation with mevalonic acid. 3 Pretreatment of cells with the heterotrimeric G protein inhibitor pertussis toxin for up to 24 h completely abolished AII-induced [Ca2+](i) rises but the response to PDGF-BB was unaffected. 4 The tyrosine kinase inhibitor genistein largely abolished PDGF-BB-induced [Ca2+](i) elevation but had no significant effect on AII-induced responses. 5 Pre-incubation with lovastatin had no effect on the level of tyrosine phosphorylation of PDGF-beta receptors (as measured by Western blot) in response to the PDGF-BB ligand. 6 PDGF-BB elicits Ca2+ influx via a tyrosine kinase-dependent mechanism distinct from the heterotrimeric G protein coupled pathway utilized by AII. Lovastatin most likely acts by inhibition of isoprenylation (via blockade of isoprenoid synthesis) of an intermediate molecule involved in PDGF-BB-induced Ca2+ influx.