Aim: 

Vasopressin (VP) binds to its type 2 receptor (V2R) and increases phosphorylation of the kidney collecting duct water channel aquaporin-2 (AQP2) at three different sites; (pS256, pS264 and pS269) and causes AQP2 apical membrane accumulation. The present aim was to identify VP independent pathways for AQP2 phosphorylation and apical membrane accumulation with focus on prostaglandin E2 (PGE2) receptors EP2 and EP4.

Methods: 

MDCK cells stably transfected with AQP2 underwent agonist stimulation followed by immunocytochemistry or cell surface biotinylation. Ex vivo studies were per formed on cortical tubule suspensions (CTS) and kidney slices (KS) from normal rats. In vivo studies were performed on normal wistar rats, which were treated with V2R antagonist OPC-31260 (10mg/day) throughout the study. After 12 hours, rats were additionally treated with either butaprost (3mg/kg) or solvent control every 12 hours for two days.

Results: 

PGE2 (Sigma, USA) (10^-10 M-10^-5 M) and selective agonists for EP2 (butaprost (Sigma, USA), 10^-9 M-10^-6 M) or EP4 (CAY10580 (Cayman Chemicals, USA), 10^-8 M-10^-5 M) caused AQP2 apical membrane accumulation and increased pS264-AQP2 in MDCK cells as well as pS256-AQP2 in CTS. PGE2 and b utaprost, but not CAY10580, increased pS269-AQP2 in MDCK cells. Moreover, PGE2 and butaprost caused AQP2 apical membrane accumulation in KS. Rats treated with OPC-31260 developed severe polyuria. Butaprost increased urine osmolality (265±27 vs 192±18 mosm/kg H2O on day1; 455±47 vs 285±34 on day2, p< 0.05) and reduced urine flow rate to 59% on day1 and 51% on day2 with no decline in creatinine clearance (605±84 vs 536±45 ml/min/100g).

Conclusion: 

EP2 and EP4 increase AQP2 membrane targeting in cells and in native tissue with differential effects on phosphorylation. Moreover, treatment with EP2 agonist butaprost alleviates polyuria in rats.