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 ang iotensin II (AngIV). [I-125]-AngIV binding is saturable, reversible an d distinct from angiotensin II (AngII) receptors. At 37 degrees C equi librium of [I-125]-AngIV binding is reached within 2 h. AngIV displace s [I-125]-AngIV bound to cultured rabbit cardiac fibroblasts whereas A ngII receptor-specific ligands ([Sar(1),Ile(8)]-AngII, Dup753, CGP4211 2A) 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 t he presence of the non-hydrolyzable GTP analog GTP(gamma)S [I-125]-Ang IV binding in rabbit cardiac fibroblasts was not markedly affected, wh ereas 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 unknow n, and the putative interaction of AngIV with AngII needs further char acterization.