Binding characteristics of [125I]endothelin-1 in guinea-pig trachea and its displacement by endothelin-1, endothelin-3 and endothelin (16-21).

The presence of binding sites for endothelin-1 (ET-1) and endothelin-3 (ET-3) in airway epithelium, submucosa and smooth muscle of guinea-pig trachea was investigated using in vitro autoradiography. We also examined the ability of the C-terminal hexapeptide of endothelin, ET(16-21) to inhibit specific [125I]ET-1, binding. ET-1 appeared to bind to a single class of binding sites (nH not different from unity). In contrast, nH values for ET-3 displacement of [125I]ET-1 specific binding were different from unity, suggesting that these peptides bound to more than one site. ET (16-21) did not affect [125I]ET-1 binding. The present results suggest that the binding sites identified in guinea pig airway smooth muscle may be related to receptors mediating contractile responses to the endothelins.