Darusentan (Lu-135252) is a selective endothelin receptor A (ET-A) receptor antagonist, which binds with a Ki of 1.4 nM to the ET-A receptor and a Ki of 184 nM to ET-B receptor, respectively with a 100-fold selectivity for ETA rather than ETB receptors[1]. Darusentan competes for radiolabeled endothelin binding in rat aortic vascular smooth muscle cells (RAVSMs) membranes with single-site kinetics, exhibiting a Ki of 13 nM[2].