Increased AQP2 targeting in primary cultured IMCD cells in response to angiotensin II through AT₁ receptor

Vasopressin and angiotensin II (ANG II) play a major role in renal water and Na⁺ reabsorption. We previously demonstrated that ANG II AT ₁ receptor blockade decreases dDAVP-induced water reabsorption and AQP2 levels in rats, suggesting cross talk between these two peptide hormones (Am J Physiol Renal Physiol 288: F673-F684, 2005). To directly address this issue, primary cultured inner medullary collecting duct (IMCD) cells from male Sprague-Dawley rats were treated for 15 min with 1) vehicle, 2) ANG II, 3) ANG II + the AT₁ receptor blocker candesartan, 4) dDAVP, 5) ANG II + dDAVP, or 6) ANG II + dDAVP + candesartan. Immunofluorescence microscopy revealed that 10^-8 M ANG II or 10^-11 M dDAVP (protocol 1) was associated with increased AQP2 labeling of the plasma membrane and decreased cytoplasmic labeling, respectively. cAMP levels increased significantly in response to 10^-8 M ANG II and were potentiated by cotreatment with 10^-11 M dDAVP. Consistent with this finding, immunoblotting revealed that this cotreatment significantly increased expression of phosphorylated AQP2. ANG II-induced AQP2 targeting was blocked by 10^-5 M candesartan. In protocol 2, treatment with a lower concentration of dDAVP (10^-12 M) or ANG II (10^-9 M) did not change subcellular AQP2 distribution, whereas 10^-12 M dDAVP + 10^-9 M ANG II enhanced AQP2 targeting. This effect was inhibited by cotreatment with 10^-5 M candesartan. ANG II-induced cAMP accumulation and AQP2 targeting were inhibited by inhibition of PKC activity. In conclusion, ANG II plays a role in the regulation of AQP2 targeting to the plasma membrane in IMCD cells through AT₁ receptor activation and potentiates the effect of dDAVP on AQP2 plasma membrane targeting.