| Autor: |
Handlogten ME; Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine,Gainesville, FL 32610-0224, USA., Hong SP, Westhoff CM, Weiner ID |
| Jazyk: |
angličtina |
| Zdroj: |
American journal of physiology. Renal physiology [Am J Physiol Renal Physiol] 2004 Oct; Vol. 287 (4), pp. F628-38. Date of Electronic Publication: 2004 May 18. |
| DOI: |
10.1152/ajprenal.00363.2003 |
| Abstrakt: |
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. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
|
