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Comparison of 125 I‐Angiotensin III and 125 I‐Angiotensin II Binding to Rat Brain Membranes
Author(s) -
Abhold Raymond H.,
Hanesworth Jodie M.,
Harding Joseph W.
Publication year - 1988
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1988.tb02988.x
Subject(s) - angiotensin ii , angiotensin iii , binding site , chemistry , receptor , angiotensin receptor , membrane , ligand (biochemistry) , medicine , endocrinology , renin–angiotensin system , biochemistry , biology , blood pressure
The binding of 125 I‐angiotensin III ( 125 I‐ANG III) to rat brain membranes was examined and compared with that of 125 I‐angiotensin II ( 125 I‐ANG II). Degradation of each ligand, as monitored by HPLC, was effectively inhibited using fragments of ANG III and ANG II known to have little affinity for angiotensin binding sites. Three classes of 125 I‐ANG III‐binding sites were observed based on affinity ( K D = 0.13, 1.83, and 10.16 n M ) and capacity ( B max = 1.30, 18.41, and 67.2 fmol/mg protein, respectively). Two classes of 125 I‐ANG II‐binding sites of high affinity ( K D = 0.11 and 1.76 n M ) and low capacity ( B max = 1.03 and 18.86 fmol/mg protein, respectively) were also identified. Cross‐displacement studies confirmed that the two highest‐affinity 125 I‐ANG Ill‐binding sites and the 125 I‐ANG II‐binding sites were the same. On the other hand, the binding of 125 I‐ANG III to the low‐affinity 125 I‐ANG III‐binding site could not be inhibited with ANG II. These data imply that previously measured differences in the biological potency of cerebroventricularly applied ANG III and ANG II probably do not result from differential binding of these pep‐tides to central angiotensin receptors.