Angiotensin II binding to renomedullary interstitial cells is regulated byosmolality

Angiotensin II (Ang II) AT(1A) receptors are localized to renomedullary int erstitial cells (RMIC) in the inner stripe of the outer medulla but not in the inner medulla. Thus, there seems to be a correlation between decreases in AT(1A) receptor binding to RMIC and increases in interstitial osmolality , suggesting that osmolality is important in determining Ang II binding to RMIC. Cultured RMIC were incubated in media of differing osmolalities (330, 630, 930, and 1230 mOsm/ kgH(2)O). I-125-[Sar(1), Ile(8)] Ang II binding t o AT(1A) receptors on RMIC grown in hyperosmolal media (930 mOsm/kgH(2)O) w as reduced compared with isoosmolal(330 mOsm/kgH(2)O) media and was progres sively reduced with further increases of osmolality. Similar studies were p erformed using bradykinin (BK) as a control peptide. Binding of the BK rece ptor ligand I-125- [HPP-Hoe 140] to B-2 receptors was not affected by varyi ng osmolality of the media. Reverse transcriptase-PCR demonstrated the pres ence of the mRNA expression for both AT(1A) and B-2 receptors at each osmol ality. The conclusion is that osmolality modulates Ang II binding to RMIC; in these cells, this phenomenon is restricted to Ang II as BK binding is no t affected. Osmolality-induced changes in Ang II binding may modulate the a ctions of this peptide on RMIC and provide an important mechanism by which these cells modulate renal medullary function.