Platelet-derived growth factor (PDGF) and angiotensin II (All) are thought to medi'ite their biological effects in vascular smooth muscle cells (VSMCs) by causing alterations in cytosolic free calcium (ICaL-],). In this study we examine the pathways b y which PDGF and All 'ilter l C a L f \ , in VSMCs. Addition of PDGF resulted in a rapid, transient, concentration-dependent increase in [Ca' 1,; this rise in [Ca" 1, was blocked conipletely by preincubation of cells with ethylene glycol-bis ((J-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) or CoCI,, by the voltage-sensitive Ca'+-channel antagonists veraparriil or nifedipine, by 12-O-tetradecanoylphorbol-I 3-acetate (TPA), or by pertussis toxin. All also caused an increase in [Ca' ' 1,; however, Ail-stimulated '\Iterations in [Ca' ' I , displayed different kinetics compared with those caused by PDCF. Pretreatment of cells with 8-(diethylnmine)-octyl-3,4,5-trimethyoxyber~zoate hydrochloride (TMB-8), almost totally inhibited All-induced increases in [C:aLi I,. EGTA or CoCI? only slightly diminished All-stimulated increases iii lCa2 ' I,. Nifedipine, verapamil, TPA, and pertussis toxin pretreatment were without effect on All-induced increases in [Ca'+I,. PDGF and All both stimulated increases in total inositol phosphate accumulation, although the one-half maximal concentration (ED,,,) for
alterations in [Ca' ' 1, and phosphoinisitide hydrolysis differed by a factor of 10 for PDGF ( 3 x 10-I" M for Ca'+ vs. 2.5 X 10 -" M for phosphoinositide hydrolysis), but they were essentially identical for All (7.5 x lo-" M for Ca' ' vs. 5.0 X l o -' M for phosphoinositide hydrolysis). PDGF stimulated mitogenesis (as measured by 1 'HI-thymidine incorporation into DNA) in VSMCs with an ED3,, similar to that for PDGF-induced ')Iterations in phosphoinositide hydrolysis. PDGF-stimulated mitogenesis was blocked by pretreatment of cells with voltage-sensitive Ca'+ channel blot kers, TPA, or pertusis toxin. These results suggest that PDGF and All cause alterations in [Ca" 1, in VSMCs by at least quantitatively distinct mechanisms. PDLF binding activates a pertussis-toxin-sensitive CaL+ influx into cells via voltcige-sensitive Ca' ' channels (blocketl by EGTA, verapainil, and nifedipine), as well as stimulating phosphoinositide hydrolysis leading to release of' Ca' ' from intracellular stores. All-induced alterations in ICa" 1, are mainly the result o i phosphoinositide hydrolysis and consequent entry of Ca' ' into the cytoplasm from intrcm41ular stores. Our data also suggest that changes in ICa'+],
caused by PDGF are required for PDGF-stimulated mitogenesis.
Alterations in vascular smooth muscle cell (VSMC) function are thought to play a role in the etiology of atherosclerosis and hypertension (