Effects of increasing concentrations of unlabeled competing ligands, Hpp-Aca-SDKP (A) and Ac-SDKP (B), or excess concentrations (10 μM) of Ac-SDKP, Hpp-Aca-SDKP, SDKP (dehydro), SDK, ET-1, and ANG II (C) on specific 125I-Hpp-Aca-SDKP receptor binding in cultured rat CFs, representing 4 different experiments. Ki, inhibition constant. Note that the inhibitory potencies of these compounds on 125I-Hpp-Aca-SDKP receptor binding were in the order of Hpp-Aca-SDKP ≥ Ac-SDKP > SDK > SDKP (dehydro) and that unrelated peptide ET-1 and ANG II did not displace 125I-Hpp-Aca-SDKP receptor binding in CFs. **P < 0.01 vs. total binding.