title: Epac regulates UT-A1 to increase urea transport in inner medullary collecting ducts.
abstract: Urea plays a critical role in the concentration of urine, thereby regulating water balance. Vasopressin, acting through cAMP, stimulates urea transport across rat terminal inner medullary collecting ducts (IMCD) by increasing the phosphorylation and accumulation at the apical plasma membrane of UT-A1. In addition to acting through protein kinase A (PKA), cAMP also activates Epac (exchange protein activated by cAMP). In this study, we tested whether the regulation of urea transport and UT-A1 transporter activity involve Epac in rat IMCD. Functional analysis showed that an Epac activator significantly increased urea permeability in isolated, perfused rat terminal IMCD. Similarly, stimulating Epac by adding forskolin and an inhibitor of PKA significantly increased urea permeability. Incubation of rat IMCD suspensions with the Epac activator significantly increased UT-A1 phosphorylation and its accumulation in the plasma membrane. Furthermore, forskolin-stimulated cAMP significantly increased ERK 1/2 phosphorylation, which was not prevented by inhibiting PKA, indicating that Epac mediated this phosphorylation of ERK 1/2. Inhibition of MEK 1/2 phosphorylation decreased the forskolin-stimulated UT-A1 phosphorylation. Taken together, activation of Epac increases urea transport, accumulation of UT-A1 at the plasma membrane, and UT-A1 phosphorylation, the latter of which is mediated by the MEK-ERK pathway.
authors: Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors: Yanhua
authors: Y
authors: Wang
authors: Janet D
authors: JD
authors: Klein
authors: Mitsi A
authors: MA
authors: Blount
authors: Christopher F
authors: CF
authors: Martin
authors: Kimilia J
authors: KJ
authors: Kent
authors: Vladimir
authors: V
authors: Pech
authors: Susan M
authors: SM
authors: Wall
authors: Jeff M
authors: JM
authors: Sands
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D007679:Kidney Medulla / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D008297:Male; D026901:Membrane Transport Proteins / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013449:Sulfonamides / Q000494:pharmacology; D014508:Urea / Q000378:metabolism*; D014667:Vasopressins / Q000378:metabolism; D000096982:Urea Transporters
chemical_list: D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020662:Guanine Nucleotide Exchange Factors; D007546:Isoquinolines; D026901:Membrane Transport Proteins; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D014508:Urea; D014667:Vasopressins; D000096982:Urea Transporters; C526973:Rapgef3 protein, rat; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide