title: Regulation of aquaporin-2 trafficking by vasopressin in the renal collecting duct. Roles of ryanodine-sensitive Ca2+ stores and calmodulin.
abstract: In the renal collecting duct, vasopressin increases osmotic water permeability (P(f)) by triggering trafficking of aquaporin-2 vesicles to the apical plasma membrane. We investigated the role of vasopressin-induced intracellular Ca(2+) 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 [Ca(2+)](i) (fluo-4). Vasopressin-induced Ca(2+) mobilization was completely blocked by preloading with the Ca(2+) chelator BAPTA. In parallel experiments, BAPTA completely blocked the vasopressin-induced increase in P(f) 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 Ca(2+) 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 microm), a ryanodine receptor antagonist, blocked the arginine vasopressin-mediated increase in P(f) 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 P(f) response to vasopressin and the vasopressin-stimulated redistribution of aquaporin-2. The results suggest that Ca(2+) release from ryanodine-sensitive stores plays an essential role in vasopressin-mediated aquaporin-2 trafficking via a calmodulin-dependent mechanism.
authors.affiliation: Laboratory of Kidney and Electrolyte Metabolism, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Chou
authors.forename: K P
authors.initials: KP
authors.lastname: Yip
authors.forename: L
authors.initials: L
authors.lastname: Michea
authors.forename: K
authors.initials: K
authors.lastname: Kador
authors.forename: J D
authors.initials: JD
authors.lastname: Ferraris
authors.forename: J B
authors.initials: JB
authors.lastname: Wade
authors.forename: M A
authors.initials: MA
authors.lastname: Knepper
mesh_terms: D000818:Animals; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins / Q000378:metabolism*; D001127:Arginine Vasopressin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012433:Ryanodine / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D014667:Vasopressins / Q000378:metabolism*
chemical_list: C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D002147:Calmodulin; D019837:Ryanodine Receptor Calcium Release Channel; D014667:Vasopressins; D001127:Arginine Vasopressin; D012433:Ryanodine; D000242:Cyclic AMP; D002118:Calcium