title: Kinetics of urea and water permeability activation by vasopressin in rat terminal IMCD.
abstract: The vasopressin-regulated urea carrier and the vasopressin-regulated water channel are distinct transporters present in the apical membrane of the inner medullary collecting duct (IMCD) cells. To assess whether these transporters may be activated by common mechanisms, we investigated the time course of increase of urea and water permeability in response to vasopressin in isolated perfused terminal IMCD segments. The permeability responses were determined through the use of a specially designed continuous-flow fluorometer for rapid analysis of collected tubule fluid samples. The time courses of activation of the two transporters by vasopressin were virtually identical. Both urea and water permeability displayed a rapid initial increase for the first 10 min followed by a slower secondary response lasting at least 30 additional min. The lag periods between vasopressin addition and the initial rise in permeability were the same for urea (34.2 +/- 8.8 s) and water (34.8 +/- 8.9 s) transport activation. Furthermore, the initial rate of permeability increase (normalized by the total increase) was not significantly different for the two transport processes. The lag periods for the increase in urea permeability in response to 8-bromoadenosine 3',5'-cyclic monophosphate and vasopressin were not significantly different. The results are consistent with the view that the rate-limiting step in vasopressin-induced activation is the same for both the urea carrier and water channel and may lie at a step beyond generation of adenosine 3',5'-cyclic monophosphate.
authors.affiliation: Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: S M
authors.initials: SM
authors.lastname: Wall
authors.forename: J S
authors.initials: JS
authors.lastname: Han
authors.forename: C L
authors.initials: CL
authors.lastname: Chou
authors.forename: M A
authors.initials: MA
authors.lastname: Knepper
mesh_terms: D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D001834:Body Water / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009995:Osmosis / Q000187:drug effects; D010539:Permeability; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014508:Urea / Q000493:pharmacokinetics*
chemical_list: D001127:Arginine Vasopressin; D014508:Urea; D000242:Cyclic AMP