Long-term vasopressin-V2-receptor stimulation induces regulation of aquaporin 4 protein in renal inner medulla and cortex of Brattleboro rats.

BACKGROUND: Desmopressin (dDAVP) induces a decrease in immunolabelling of aquaporin (AQP) 4 protein in the terminal inner medulla (IM) of the Brattleboro (BB) rat kidney. It is disputed, however, whether the decreased labelling reflects real down-regulation of protein abundance, or whether it is a result of epitope shielding in the AQP4 protein, preventing binding of the antibody as previously suggested. Furthermore, it is unknown if vasopressin regulates AQP4 in the connecting tubule (CNT) and in the cortical collecting duct (CCD). Using BB rats, we aimed to determine (i) whether the dDAVP-induced decrease in AQP4 labelling in the terminal IM reflects down-regulation in protein abundance and (ii) whether dDAVP increases the AQP4 protein abundance in the CNT and the CCD.

METHODS: BB rats received dDAVP or saline (control) via osmotic minipumps pumps for 6 days.

RESULTS: Immunolight microscopy revealed strong AQP4 labelling in the initial inner medullary collecting duct (IMCD1), weak labelling in the middle IMCD (IMCD2) and weak/absent labelling in the terminal IMCD (IMCD3) after 6 days of dDAVP administration. AQP3 labelling was similar to that of AQP4. Two-hour administration with dDAVP (previously described BB rats) did not change the labelling pattern of AQP4, suggesting that potential acute phosphorylation did not induce epitope shielding, thereby preventing the binding of the antibody.

CONCLUSIONS: In BB rats, long-term administration with dDAVP (i) increased the AQP4 protein abundance in the IMCD1 and decreased the abundance in the IMCD2 and the IMCD3, and (ii) increased the AQP4 protein abundance in the CNT and the CCD.