Regulation of Aquaporin-2 Trafficking by Vasopressin in the Renal Collecting Duct

Title: Regulation of Aquaporin-2 Trafficking by Vasopressin in the Renal Collecting Duct
Authors: Chou, Chung-Lin; Yip, Kay-Pong; Michea, Luis; Kador, Karl; Ferraris, Joan D.; Wade, James B.; Knepper, Mark
Publisher: Journal of Biological Chemistry
Date Published: November 24, 2000
Reference Number: 535
In the renal collecting duct, vasopressin increases osmotic water permeability (Pf) by triggering trafficking of aquaporin-2 vesicles to the apical plasma membrane. We investigated the role of vasopressin-induced intracellular Ca2+ mobilization in this process. In isolated inner medullary collecting ducts (IMCDs), vasopressin (0.1 nM) and 8-(4-chlorophenylthio)-cAMP (0.1 mM) elicited marked increases in [Ca2+]i (fluo-4). Vasopressin-induced Ca2+ mobilization was completely blocked by preloading with the Ca2+ chelator BAPTA. In parallel experiments, BAPTA completely blocked the vasopressin-induced increase in Pf without affecting adenosine 3',5'-cyclic monophosphate (cAMP) production. Previously, we demonstrated the lack of activation of the phosphoinositide-signaling pathway by vasopressin in IMCD, suggesting an inositol 1,4,5-trisphosphate-independent mechanism of Ca2+ release. Evidence for expression of the type 1 ryanodine receptor (RyR1) in IMCD was obtained by immunofluorescence, immunoblotting, and reverse transcription-polymerase chain reaction. Ryanodine (100 ?M), a ryanodine receptor antagonist, blocked the arginine vasopressin-mediated increase in Pf and blocked vasopressin-stimulated redistribution of aquaporin-2 to the plasma membrane domain in primary cultures of IMCD cells, as assessed by immunofluorescence immunocytochemistry. Calmodulin inhibitors (W7 and trifluoperazine) blocked the Pf response to vasopressin and the vasopressin-stimulated redistribution of aquaporin-2. The results suggest that Ca2+ release from ryanodine-sensitive stores plays an essential role in vasopressin-mediated aquaporin-2 trafficking via a calmodulin-dependent mechanism.
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