Regulation of receptor binding interactions of 125I-angiotensin II and 125I-[sarcosine1,leucine8]angiotensin II, an angiotensin antagonist, by sodium ion.

Angiotensin receptor binding interactions of the angiotensin agonist, 125I-angiotensin II (125I-AII), and antagonist, 125I-[sarcosine1,leucine8]angiotensin II (125I[Sar1,Leu8]AII), are differentially affected by sodium ion concentration. 125I-AII binding to calf cerebellar cortex or adrenal cortex is increased 25 or 2.5 fold respectively when sodium ion concentration is increased from 10 to 150 mM. In brain membranes increasing sodium concentration accelerates the association and slows the dissociation of 125I-AII. 125I[Sar1,Leu8]AII binding to these tissues is much less sensitive to changes in sodium ion concentration. In rabbit uterine homogenates, neither 125I-AII nor 125I[Sar1,Leu8]AII binding is significantly altered by changes in sodium ion concentration. The sodium elicited increase in 125I-AII binding to calf cerebellum is correlated with cationic size and is not an ionic strength effect. The effect of sodium on potencies of angiotensin analogues in competing for 125I[Sar1,Leu8]AII binding does not correlate with agonist or antagonist properties, but is largest for peptides with aspartic acid at position one in the peptide structure.