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Identification of a novel, brain‐specific, non‐AT1, non‐AT2 binding site for angiotensins in the mouse brain
Author(s) -
Karamyan Vardan T.,
Speth Robert C
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a432-c
Subject(s) - losartan , angiotensin ii , binding site , chemistry , angiotensin ii receptor type 1 , hypothalamus , medicine , endocrinology , receptor , angiotensin iii , renin–angiotensin system , microbiology and biotechnology , biology , biochemistry , blood pressure
We recently described a novel, non‐AT1, non‐AT2 binding site for angiotensin II (Ang II) in rat brain (Karamyan and Speth, Soc. Neuroscience Abstracts 2006, Prog. # 453.7). We now report additional characterization of this binding site. Conditions previously established for its expression in rat brain were used to determine if it also exists in male Swiss‐Webster mouse brain: incubation of 125 I‐Ang II for 1 hr at 24 C with brain membranes in assay buffer: 5 mM EDTA, 150 mM NaCl, 0.1 mM bacitracin and 50 mM NaPO 4 (pH 7.2), 10 μM PD123319 and losartan, and 0.3 mM p‐chloromercuribenzoic acid (PCMB). The binding site was present in both the hypothalamus (B max = 1.43±0.13 fmol/mg wet wt., K D = 2.8±0.6 nM) and cerebral cortex (B max = 1.94±0.16 fmol/mg wet wt., K D = 3.4±0.6 nM), of the mouse brain, but it was not present in the liver. HPLC analysis of bound 125 I in rat hypothalamus revealed that the presence of PCMB in the assay buffer preserved 38% of the 125 I‐Ang II compared to just 3% in its absence. Consistent with partial protection of 125 I‐Ang II, a time course of 125 I‐Ang II binding to rat brain showed maximum binding at 45 – 60 min, after which it declined 25% at 2 hrs. This increases the apparent K D , underestimating the binding affinity. These observations confirm the presence of this brain‐specific, high affinity, non‐AT1, non‐AT2 binding site in the mouse. This site may have therapeutic relevance for the treatment of hypertension.