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Abstract

Endothelins (EIS), potent vasoconstrictors, are also neuropeptides in mammalian brain. The objectives of this study were to identify and characterize the receptors for ETs in rat cerebellum, using radioligand binding techniques and affinity cross-linking method. Iodinated ET-1 bound specifically to receptors in rat cerebellar membrane in a dose-dependent manner. Scatchard plot indicated a single class of high-affinity binding sites. Apparent Kd value was 110 pM, and the Bmax value was 4.85 pmol/mg of membrane protein. Through experiments of affinity cross-linking of ET receptors with 125I-ET-1, two forms of endothelin receptors with molecular masses of 47 KD and 32 KD were identified. Electrophoresis conducted in the presence of reducing reagents did not affect the mobilities of specifically labeled bands, suggesting that endothelin receptors exist as a single polypeptide chain. The order of potency for EIS and sarafotoxin 6b (S6b) in displacing the specifically bound iodinated ET-1 from cerebellar membrane was ET-1 = ET-2 = ET-3 >S6b. Result from receptor specificity indicated that endothelin receptors in rat cerebellum belong to endothelin receptor subtype B.

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