title: Apical ammonia transport by the mouse inner medullary collecting duct cell (mIMCD-3).
abstract: The collecting duct is the primary site of urinary ammonia secretion; the current study determines whether apical ammonia transport in the mouse inner medullary collecting duct cell (mIMCD-3) occurs via nonionic diffusion or a transporter-mediated process and, if the latter, presents the characteristics of this apical ammonia transport. We used confluent cells on permeable support membranes and examined apical uptake of the ammonia analog [(14)C]methylammonia ([(14)C]MA). mIMCD-3 cells exhibited both diffusive and saturable, transporter-mediated, nondiffusive apical [(14)C]MA transport. Transporter-mediated [(14)C]MA uptake had a K(m) of 7.0 +/- 1.5 mM and was competitively inhibited by ammonia with a K(i) of 4.3 +/- 2.0 mM. Transport activity was stimulated by both intracellular acidification and extracellular alkalinization, and it was unaltered by changes in membrane voltage, thereby functionally identifying an apical, electroneutral NH(4)(+)/H(+) exchange activity. Transport was bidirectional, consistent with a role in ammonia secretion. In addition, transport was not altered by Na(+) or K(+) removal, not inhibited by luminal K(+), and not mediated by apical H(+)-K(+)-ATPase, Na(+)-K(+)-ATPase, or Na(+)/H(+) exchange. Finally, mIMCD-3 cells express the recently identified ammonia transporter family member Rh C glycoprotein (RhCG) at its apical membrane. These studies indicate that the renal collecting duct cell mIMCD-3 has a novel apical, electroneutral Na(+)- and K(+)-independent NH(4)(+)/H(+) exchange activity, possibly mediated by RhCG, that is likely to mediate important components of collecting duct ammonia secretion.
authors.affiliation: Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, 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: D000143:Acids / Q000494:pharmacology; D000465:Algorithms; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001693:Biological Transport, Active; D001710:Biotin / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D027682:Cation Transport Proteins / Q000378:metabolism; D002460:Cell Line; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007679:Kidney Medulla / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D008566:Membranes / Q000378:metabolism; D008744:Methylamines / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D015233:Models, Statistical; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism
chemical_list: D000143:Acids; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D008562:Membrane Glycoproteins; D008744:Methylamines; C485880:Rhcg protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D001710:Biotin; D000641:Ammonia; C027451:methylamine; D017506:H(+)-K(+)-Exchanging ATPase