Binding of KRH-594, an antagonist of the angiotensin II type 1 receptor, to cloned human and rat angiotensin II receptors

We studied the binding properties of KRH-594, a new selective antagonist of angiotensin II (AII) type 1 (AT(1)) receptors, to rat liver membranes and to recombinant AT(1) and AT(2) receptors. Preincubation of rat liver membranes with KRH-594 produced maximal inhibition of [I-125]-AII binding when the preincubation time was 1-2 h. Preincubation with KRH-594 for 2 h decreased the B-max value and increased the K-d value. For human AT(1), human AT(2), rat AT(1A) and rat AT(1B) receptors, the K-i values for KRH-594 were 1.24, 9360, 0.67, and 1.02 nm, respectively. The rank order of K-i values for human AT(1) receptors was KRH-594 >> EXP3174 > candesartan = AII. The order of specificities for human AT(1) and AT(2) receptors was candesartan > EXP3174 > KRH-594. Although a 2-h preincubation of human AT(2) receptors with KRH-594 (30 muM) or CGP 42112 (a selective AT(2) receptor antagonist; 0.3 nm) inhibited binding of [I-125]-AII, the suppression by KRH-594 was not significant. These results indicate that KRH-594 binds potently to AT(1) receptors in an insurmountable manner, and that at a very high dose (30 muM) it may also bind to AT(2) receptors, but in a surmountable manner.