Endothelin B receptor-mediated regulation of endothelin-I content and release in cultured porcine aorta endothelial cell

Several cardiovascular diseases are associated with an increase in circulating levels of endothelin-1 (ET-1). Little is known about the consequences of this increase on endothelial cell responses with respect to ET-1 production and regulation. Confluent, passage 1, cultured porcine aorta endothelial cells were exposed to exogenous ET-1 (0.1 muM) for 24 h. BQ788 (I muM, ETB receptor antagonist) but not BQ123 (1 muM, ETA receptor antagonist) significantly (p < 0.05) reduced I-125-ET-1 uptake. The effects of BQ788 were mimicked by dansylcadaverine (0.5 mM) but not nystatin (50 mug/ml). Immunoreactive ET-1 endothelial cell content doubled (p < 0.05) after 24 11 of exogenous ET-I treatment. Bosentan (10 muM, dual ETA/B receptor antagonist) reduced (p < 0.05) immunoreactive ET-1 content in control cells. Bosentan prevented exogenous ET-1-induced endothelial cell ET-1 loading, suggesting that exogenous ET-1 is partly recycled. PreproET-1 mRNA levels were reduced (p < 0.05) by exogenous ET-1 after 24 h, an effect blocked by BQ788 and bosentan. When used alone, both receptor antagonists increased mRNA levels. The results of this study suggest that part of ET-1 is recycled through ETB receptors and subsequently released to contribute to constitutive ET-1 overflow. ET-1 exerts a negative feedback on ET-1 gene transcription, which is dependent on ETB receptor activation and internalization of the complex ET-1/ETB receptor. The maintenance of this negative regulatory loop of ET-1 production may be essential for the normal endothelial physiology.