Topographic distribution of aquaporin 2 mRNA in the kidney of dehydrated rats

Background: Stimulation of arginine vasopressin results in an immediate red istribution of water channels (aqua-porin 2; AQP2) in the apical membrane o f the collecting ducts, leading to water reabsorption. Water restriction fo r greater than or equal to 24 h increases AQP2 proteins in the whole collec ting duct which is highest in the inner medulla of the kidney, indicating t hat dehydration enhances synthesis of this protein. Although increased expr ession of AQP2 mRNA under this condition has been reported, the increased r atio of mRNA expression in the th ree regions of the kidney, cortex, outer medulla, and inner medulla, during the dehydration is still unclear. Method s: We investigated the AQP2 transcripts using male Sprague-Dawley rats depr ived of water for 24 h. Mimic cDNA for competitive polymerase chain reactio n (PCR) was constructed by deleting 180 bp at the middle of a 780-bp partia l PCR product for rat AQP2 cDNA. In situ hybridization of the kidney and No rthern blotting of inner medulla were performed using a 60-bp oligo-cDNA pr obe which identified rat AQP2 transcripts in the collecting duct. Results: Dehydration resulted in a significant increase in plasma osmolality and arg inine vasopressin concentration and urinary osmolality. Competitive PCR dem onstrated that dehydration increased AQP2 transcripts in all parts of the k idney, but was highest in the inner medulla. Northern blotting confirmed th e high increased rate of AQP2 transcription in the inner medulla. In situ h ybridization showed markedly intensified signals in the inner medulla of de hydrated rats. Conclusions: Our data indicate that dehydration increases th e abundance of AQP2 transcripts which may be closely associated with enhanc ement in AQP2 protein synthesis reported previously. This topographically v ariable increase in transcription is considered to be one of the mechanisms involved in long-term regulation of water permeability in the collecting d uct. Copyright (C) 2000 S. Karger AG. Basel.