125I-Angiotensin 1-7 binds to a different site than angiotensin 1-7 in tissue membrane preparations
- Endocrine. 2021 May;72(2):529-538. doi: 10.1007/s12020-020-02572-2.
- 1. College of Pharmacy, Nova Southeastern University, Fort Lauderdale, FL, USA.
- 2. Department of Surgery, University of Miami, Miami, FL, USA.
- 3. Halmos College of Natural Science & Oceanography, Nova Southeastern University, Fort Lauderdale, FL, USA.
- 4. Kiran P. Patel College of Osteopathic Medicine, Nova Southeastern University, Fort Lauderdale, FL, USA.
- 5. Institute for Neuro-Immune Medicine, Nova Southeastern University, Fort Lauderdale, FL, USA.
- 6. Laboratório de Fisiologia Translacional, Universidade Federal de Ciências da Saúde de Porto, Alegre, RS, Brazil.
- 7. Department of Biology, Appalachian State University, North Carolina Research Campus, Kannapolis, NC, USA.
- 8. College of Pharmacy, Nova Southeastern University, Fort Lauderdale, FL, USA. [email protected].
- 9. Department of Pharmacology and Physiology, School of Medicine, Georgetown University, Washington, DC, USA. [email protected].
Purpose: To study the receptor for Angiotensin (Ang) 1-7 using a radioligand (125I-Ang 1-7)-binding assay. For more than a decade, Mas has been viewed as the receptor for Ang 1-7; however, Ang 1-7 binding has not been pharmacologically characterized in tissue membrane preparations.
Methods: Radioligand-binding assays were carried out using tissue membrane preparations using radioiodinated Angiotensin 1-7 (125I-Ang 1-7) to characterize its binding site. Non-radioactive 127I-Ang 1-7 was used to test if the addition of an iodine to the tyrosine4 moiety of Ang 1-7 changes the ability of Ang 1-7 to competitively inhibit 125I-Ang 1-7 binding.
Results: 125I-Ang 1-7 binds saturably, with moderately high affinity (10-20 nM) to a binding site in rat liver membranes that is displaceable by 127I-Ang 1-7 at nanomolar concentrations (IC50 = 62 nM) while Ang 1-7 displaces at micromolar concentrations (IC50 = 80 µM) at ~22 °C. This binding was also displaceable by inhibitors of metalloproteases at room temperature. This suggests that 125I-Ang 1-7 binds to MMPs and/or ADAMs as well as Other liver membrane elements at ~ 22 °C. However, when 125I-Ang 1-7-binding assays were run at 0-4 °C, the same MMP inhibitors did not effectively compete for 125I-Ang 1-7.
Conclusions: The addition of an iodine molecule to the tyrosine in position 4 of Ang 1-7 drastically changes the binding characteristics of this peptide making it unsuitable for characterization of Ang 1-7 receptors.