Endothelin-1 stimulates proliferation of human coronary smooth muscle cells via the ET_A receptor and is co-mitogenic with growth factors

We investigated the effects of endothelin-1 (ET-1) on growth of cultured human coronary artery smooth muscle cells (cSMC). ET-1 alone stimulated DNA synthesis in growth-arrested cSMC as measured by [³H]thymidine incorporation, with a maximum 63±23% increase above control by 10^-7 M (P<0.05). ET-1 (10^-7 M) also stimulated increases in cyclin D1 protein levels after 24 h, and in absolute cell number after 4 days. Furthermore, ET-1 stimulated protein synthesis (maximum 73±32% increase in [³H]leucine incorporation by 10^-7 M (P<0.05)), as well as triggering intracellular calcium transients in human cSMC, as visualised under fura-2 fluorescence microscopy. The selective ET_A receptor antagonist BQ123 inhibited the increases in DNA synthesis, cell number, protein synthesis and intracellular calcium concentration in response to ET-1, whereas the ET_B receptor antagonist BQ788 had no such effects. Furthermore, the ETB agonist sarafotoxin 6c had no effect on cSMC DNA synthesis. In addition, co-incubation of ET-1 with threshold concentrations of the growth factors, platelet-derived growth factor-BB (PDGF-BB), basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF), resulted in pronounced synergistic increases in DNA synthesis over that observed with the factors alone. In conclusion, we have shown that ET-1 stimulates proliferation of human cSMC via the ET_A receptor and is also a co-mitogen with the growth factors tested. These findings indicate a role for ET-1 in the development of coronary intimal hyperplasia in man.