ENDOTHELIN-1-SELECTIVE BINDING-SITES ARE DOWN-REGULATED BY TRANSFORMING GROWTH-FACTOR-BETA AND UP-REGULATED BY BASIC FIBROBLAST GROWTH-FACTOR IN A VASCULAR SMOOTH MUSCLE-DERIVED CELL-LINE

Endothelins (ETs) elicit in vivo and in vitro a potent vasoconstrictor activity after binding to high-affinity receptors on vascular smooth muscle cells (VSMC). A617 cells, a VSM-derived cell line, were used as an in vitro model system to study selected growth factors and cytokines involved in proliferative and/or inflammatory diseases of the vessel wall as possible regulators of the high-affinity binding capacity of ET-1 to the cells. Radioligand studies characterized the binding of ET-1 to the isopeptide selective ET(A) receptor subtype on A617 cells as a time- and temperature-dependent saturable process (K-d = 0.13 +/- 0.04 nM, B-max = 49 +/- 7 fmol/10(6) cells). Pretreatment of A617 cells with basic fibroblast growth factor (bFGF), a mitogenic agent for vascular cells, resulted in a time- and dose-dependent increase in ET-1 binding capacity, whereas preexposure to transforming growth factor-beta (TGF-beta) induced a reduction of the B-max for ET-1. Platelet-derived growth factor (PDGF), interleukin-6 (IL-6), tumor necrosis factor-alpha, and fetal bovine serum (FBS) pretreatments did not affect consequent ET-1 binding to A617 cells.