| pubmed-article:1725304 | pubmed:abstractText | Scatchard-plot analysis of [125I]ET-1 and [125I]ET-3 binding to rat lung membranes exhibited almost the same Kd values whereas the concentration of the binding sites of ET-1 is approximately four times higher than that of ET-3. This result suggests the presence of at least two distinct subtypes of ET receptors: an ET-1-specific type and an ET-3-specific or ET-1 and ET-3 nonselective type. On the other hand, in rat brain membranes, a curvilinear Scatchard plot was obtained for [125I]ET-3 in contrast to a linear plot for [125I]ET-1. This finding also demonstrates the existence of the two different receptor subtypes having the same affinity for ET-1, but one of which has a high affinity and the other has a low affinity for ET-3. Moreover, these data indicate that an ET receptor subtype exists in rat brain different from the subtype in rat lung. To obtain the bases for a further detailed characterization of the receptor, we have purified the rat lung ET receptor to homogeneity by ET-1-affinity chromatography. The purified receptor exhibits a molecular mass of 45 kDa, in good agreement with that estimated from the affinity labeling. | lld:pubmed |
