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PMID:15798090

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Citation

Handlogten, ME, Hong, SP, Westhoff, CM and Weiner, ID (2005) Apical ammonia transport by the mouse inner medullary collecting duct cell (mIMCD-3). Am. J. Physiol. Renal Physiol. 289:F347-58

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.

Links

PubMed Online version:10.1152/ajprenal.00253.2004

Keywords

Acids/pharmacology; Algorithms; Ammonia/metabolism; Animals; Binding, Competitive/drug effects; Biological Transport, Active; Biotin/metabolism; Carrier Proteins/metabolism; Cation Transport Proteins/metabolism; Cell Line; H(+)-K(+)-Exchanging ATPase/metabolism; Hydrogen-Ion Concentration; Immunoblotting; Kidney Medulla/metabolism; Kidney Tubules, Collecting/metabolism; Membrane Glycoproteins/metabolism; Membrane Potentials/physiology; Membranes/metabolism; Methylamines/metabolism; Mice; Microscopy, Fluorescence; Models, Statistical; Reverse Transcriptase Polymerase Chain Reaction; Sodium-Hydrogen Antiporter/metabolism

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

MOUSE:RHBG

located_in

GO:0016323: basolateral plasma membrane

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete

MOUSE:RHCG

involved_in

GO:0015696: ammonium transport

ECO:0000314: direct assay evidence used in manual assertion

P

Seeded From UniProt

complete

MOUSE:RHCG

enables

GO:0008519: ammonium transmembrane transporter activity

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete

MOUSE:RHCG

located_in

GO:0016324: apical plasma membrane

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete


See also

References

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