title: Coupling of vasopressin-induced intracellular Ca2+ mobilization and apical exocytosis in perfused rat kidney collecting duct.
abstract: Arginine vasopressin (AVP) regulates the osmotic water permeability of the kidney collecting duct by inducing exocytotic insertion of aquaporin-2 into apical membrane. The coupling between AVP-induced intracellular Ca2+ mobilization and apical exocytosis was investigated in isolated perfused rat inner medullary collecting duct (IMCD) segments using confocal fluorescence microscopy. Changes of [Ca2+]i in IMCD cells were measured with fluo-4. A novel confocal imaging technique using a styryl dye, FM1-43, was developed to monitor real-time exocytosis induced by arginine vasopressin. AVP (0.1 nM) triggered a rapid increase of [Ca2+]i in IMCD cells, followed by sustained oscillations. Ratiometric measurement of [Ca2+]i confirmed that the observed [Ca2+]i oscillation was a primary event and was not secondary to changes in cell volume. The frequencies of [Ca2+]i oscillations in each IMCD cell were independent and time variant. 1-Deamino-8-D-arginine vasopressin (a V2 receptor agonist, 0.1 nM) simulated the effects of AVP by triggering [Ca2+]i oscillations. In the absence of extracellular Ca2+, ryanodine (0.1 mM) inhibited AVP-induced Ca2+ mobilization. AVP (0.1 nM) triggered accumulative apical exocytosis in IMCD cells within 20 s after application. Pre-incubating the IMCD with an intracellular Ca2+ chelator, BAPTA, prevented AVP-induced intracellular Ca2+ mobilization, apical exocytosis, and increase of osmotic water permeability. These results indicate that AVP, via the V2 receptor, triggers a calcium signalling cascade observed as [Ca2+]i oscillations in the IMCD and that intracellular Ca2+ mobilization is required for exocytotic insertion of aquaporin-2.
authors.affiliation: Department of Physiology and Biophysics, College of Medicine, University of South Florida, Tampa, FL 33612, USA. dyip@hsc.usf.edu
authors.forename: Kay-Pong
authors.initials: KP
authors.lastname: Yip
mesh_terms: D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008297:Male; D009991:Oscillometry; D010477:Perfusion; D051381:Rats; D017207:Rats, Sprague-Dawley; D012076:Renal Agents / Q000494:pharmacology*
chemical_list: D012076:Renal Agents; D001127:Arginine Vasopressin; D002118:Calcium