title: Basolateral ammonium transport by the mouse inner medullary collecting duct cell (mIMCD-3).
abstract: The renal collecting duct is the primary site for the ammonia secretion necessary for acid-base homeostasis. Recent studies have identified the presence of putative ammonia transporters in the collecting duct, but whether the collecting duct has transporter-mediated ammonia transport is unknown. The purpose of this study was to examine basolateral ammonia transport in the mouse collecting duct cell (mIMCD-3). To examine mIMCD-3 basolateral ammonia transport, we used cells grown to confluence on permeable support membranes and quantified basolateral uptake of the radiolabeled ammonia analog [14C]methylammonia ([14C]MA). mIMCD-3 cell basolateral MA transport exhibited both diffusive and transporter-mediated components. Transporter-mediated uptake exhibited a Km for MA of 4.6 +/- 0.2 mM, exceeded diffusive uptake at MA concentrations below 7.0 +/- 1.8 mM, and was competitively inhibited by ammonia with a Ki of 2.1 +/- 0.6 mM. Transporter-mediated uptake was not altered by inhibitors of Na+-K+-ATPase, Na+-K+-2Cl(-) cotransporter, K+ channels or KCC proteins, by excess potassium, by extracellular sodium or potassium removal or by varying membrane potential, suggesting the presence of a novel, electroneutral ammonia-MA transport mechanism. Increasing the outwardly directed transmembrane H+ gradient increased transport activity by increasing Vmax. Finally, mIMCD-3 cells express mRNA and protein for the putative ammonia transporter Rh B-glycoprotein (RhBG), and they exhibit basolateral RhBG immunoreactivity. We conclude that mIMCD-3 cells express a basolateral electroneutral NH4+/H+ exchange activity that may be mediated by RhBG.
authors.affiliation: Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine,Gainesville, FL 32610-0224, USA.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Handlogten
authors.forename: Seong-Pyo
authors.initials: SP
authors.lastname: Hong
authors.forename: Connie M
authors.initials: CM
authors.lastname: Westhoff
authors.forename: I David
authors.initials: ID
authors.lastname: Weiner
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D002412:Cations / Q000378:metabolism; D002460:Cell Line; D016764:Cell Polarity / Q000502:physiology; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism*; D007679:Kidney Medulla / Q000166:cytology; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D026901:Membrane Transport Proteins; D008744:Methylamines / Q000493:pharmacokinetics; D051379:Mice; D011188:Potassium / Q000378:metabolism; D011522:Protons; D000644:Quaternary Ammonium Compounds / Q000493:pharmacokinetics*; D012333:RNA, Messenger / Q000032:analysis
chemical_list: D002352:Carrier Proteins; D002412:Cations; D006023:Glycoproteins; D026901:Membrane Transport Proteins; D008744:Methylamines; D011522:Protons; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; C486033:RhBG protein, mouse; C027451:methylamine; D011188:Potassium