A SPECIFIC BINDING-SITE FOR ANGIOTENSIN II(3-8), ANGIOTENSIN-IV, IN RABBIT CARDIAC FIBROBLASTS

This study demonstrates the existence of a high affinity binding site on rabbit cardiac fibroblasts of the hexapeptide (3-8) fragment of angiotensin II (AngIV). [I-125]-AngIV binding is saturable, reversible and distinct from angiotensin II (AngII) receptors. At 37 degrees C equilibrium of [I-125]-AngIV binding is reached within 2 h. AngIV displaces [I-125]-AngIV bound to cultured rabbit cardiac fibroblasts whereas AngII receptor-specific ligands ([Sar(1),Ile(8)]-AngII, Dup753, CGP42112A) do not. Scatchard plot analysis revealed that [I-125]-AngIV binds to a single class of sites with K-d = 4.87 +/- 0.11 x 10(-9) mol/l, B-max = 371 +/- 8.3 fmol/mg protein and a Hill coefficient of 0.92. In the presence of the non-hydrolyzable GTP analog GTP(gamma)S [I-125]-AngIV binding in rabbit cardiac fibroblasts was not markedly affected, whereas binding of [I-125]-(Sar(1),Ile(8))-AngII is reduced. The role of AngIV in the heart and in particular in cardiac fibroblasts is unknown, and the putative interaction of AngIV with AngII needs further characterization.