AB3274-50UL Sigma-AldrichAnti-Aquaporin 2 Antibody

The aquaporin-2 (AQP2) vasopressin water channel is translocated to the apical membrane upon vasopressin stimulation. Phosphorylation of serine 256 of AQP2 by cAMP-dependent protein kinase has been shown, but its relation to vasopressin-regulated translocation has not been elucidated. To address this question, wild type (WT) AQP2 and a mutant with alanine in place of serine 256 of AQP2 (S256A) were expressed in LLC-PK1 cells by electroporation. Measurements by a stopped-flow light-scattering method revealed that the osmotic water permeability (Pf) of LLC-PK1 cells transfected with WT was 69.6 +/- 6.5 microm/s (24.8 +/- 2.2 microm/s for mock-transfected), and stimulation by 500 microM 8-(4-chlorophenylthio)-cAMP increased the Pf by 85 +/- 12%. When S256A AQP2 was transfected, the cAMP-dependent increase in the Pf was only 8 +/- 5%. After cAMP stimulation, the increase in surface expression of AQP2 determined by surface biotin labeling was 4 +/- 10%, significantly less than that for WT (88 +/- 5%). In addition, an in vivo [32P]orthophosphate labeling assay demonstrated significant phosphorylation of WT AQP2 and only minimal phosphorylation of S256A AQP2 in LLC-PK1 cells. Our results indicated that serine 256 of AQP2 is necessary for regulatory exocytosis and that cAMP-responsive redistribution of AQP2 may be regulated by phosphorylation of AQP2.

The molecular pathways for fluid transport in pulmonary, oral, and nasal tissues are still unresolved. Here we use immunocytochemistry and immunoelectron microscopy to define the sites of expression of four aquaporins in the respiratory tract and glandular epithelia, where they reside in distinct, nonoverlapping sites. Aquaporin-1 (AQP1) is present in apical and basolateral membranes of bronchial, tracheal, and nasopharyngeal vascular endothelium and fibroblasts. AQP5 is localized to the apical plasma membrane of type I pneumocytes and the apical plasma membranes of secretory epithelium in upper airway and salivary glands. In contrast, AQP3 is present in basal cells of tracheal and nasopharyngeal epithelium and is abundant in basolateral membranes of surface epithelial cells of nasal conchus. AQP4 resides in basolateral membranes of columnar cells of bronchial, tracheal, and nasopharyngeal epithelium; in nasal conchus AQP4 is restricted to basolateral membranes of a subset of intra- and subepithelial glands. These sites of expression suggest that transalveolar water movement, modulation of airway surface liquid, air humidification, and generation of nasopharyngeal secretions involve a coordinated network of aquaporin water channels.

Two kidney water channels have been identified: CHIP28 in proximal tubule and thin descending limb, and WCH-CD in collecting duct apical membrane. An homologous cDNA (WCH3) was obtained from rat kidney and found to encode a 276 amino acid, 29 kDa protein with 39% amino acid identity to rat CHIP28, 50% to WCH-CD and 49% to MIP26. The WCH3 transcript of 2.5 kb was expressed exclusively in kidney and was upregulated in dehydrated rats. Cell-free translation produced an approximately 28 kDa protein. Analysis of the predicted amino acid sequence indicated a hydrophobic protein with 4-6 membrane-spanning domains, with one N-linked glycosylation site, two conserved NPA boxes common to MIP26 family proteins, and conserved residue C189 common to water channels. WCH3 is a new member of the MIP26 family of channel-forming proteins in mammalian kidney.