BQ-123 (PMZ 2123) is a potent, selective, non-competitive cyclic pentapeptide ETA receptor antagonist with IC50 of 7.3 nM.
BQ-123 antagonizes endothelin-1-induced contractions in rabbit aorta, increases in inositol phosphates in cultured rat vascular smooth muscle A10 cells, shifts concentration-response curves in isolated rabbit aorta elicited by angiotensin II, but does not bind to angiotensin II receptors nor affect angiotensin II-induced increases in inositol phosphates.
