Endothelial cell-specific ETB receptor knockout: autoradiographic and histological characterisation and crucial role in the clearance of endothelin-1This article is one of a selection of papers published in the two-part special issue entitled 20 Years of Endothelin Research.

Abstract

Inactivation of endothelin B receptors (ETB), either through selective pharmacological antagonism or genetic mutation, increases the circulating concentration of endothelin-1 (ET-1), suggesting ETB plays an important role in clearance of this peptide. However, the cellular site of ETB-mediated clearance has not yet been determined. We have used a novel mouse model of endothelial cell-specific knockout (KO) of ETB (EC ETB–/–) to evaluate the relative contribution of EC-ETB to the clearance of ET-1. Phenotypic evidence of EC-specific ETB KO was confirmed by immunocytochemistry and autoradiography. Binding of the radiolabelled selective ETB ligand BQ3020 was significantly and selectively decreased in EC-rich tissues of EC ETB–/– mice, including the lung, liver, and kidney. By contrast, ETA binding was unaltered. RT-PCR confirmed equal expression of ET-1 in tissue from EC ETB–/– mice and controls, despite increased concentration of plasma ET-1 in EC ETB–/–. Clearance of an intravenous bolus of [125I]ET-1 was impaired in EC ETB–/– mice. Pretreatment with the selective ETB antagonist A192621 impaired [125I]ET-1 clearance in control animals to a similar extent, but did not further impair clearance in EC ETB–/– mice. These studies suggest that EC-ETB are largely responsible for the clearance of ET-1 from the circulation.