IMPORTANCE OF THE PHENOTYPIC STATE OF VASCULAR SMOOTH-MUSCLE CELLS ON THE BINDING AND THE MITOGENIC ACTIVITY OF ENDOTHELIN

Smooth muscle cells of the rabbit aorta, when grown in vitro, express distinguishable forms of phenotypes (contractile and synthetic). On contractile cells, ET-1 specifically bound to a single class of high affinity (K(D) = 128 pM) and high capacity (B(max) = 66,000 sites/cell) binding sites. But, whereas affinity of [I-125]-Et-1 was not significantly affected by phenotypic modulation, synthetic cells displayed a 10-fold lower [I-125]-ET-1 binding capacity than contractile smooth muscle cells. Similarly, the mitogenic effect of ET-1 on smooth muscle cells was considerably lower for synthetic than for contractile cells. The ET-1 receptor on primary cells was recognized by sarafotoxin S6b and the different ET-related peptides with an order of potency [ET-1 > S6b > ET-3 > Big ET-1 >> ET(16-21)] identical to that inducing smooth muscle cell growth. Therefore, these data indicate that the binding and the mitogenic effects of ET-1 on smooth muscle cells might be of different magnitudes depending on the phenotypic state of these cells.