Journal article
Sodium-bicarbonate cotransporter NBCn1 in the kidney medullary thick ascending limb cell line is upregulated under acidic conditions and enhances ammonium transport
Experimental physiology, Vol.95(9), pp.926-937
09/01/2010
DOI: 10.1113/expphysiol.2010.053967
PMCID: PMC2923243
PMID: 20591978
Abstract
In this study, we examined the effect of bicarbonate transporters on ammonium/ammonia uptake in the medullary thick ascending limb cell line ST-1. Cells were treated with 1 mm ouabain and 0.2 mm bumetanide to minimize carrier-mediated NH(4)+ transport, and the intracellular accumulation of 14C-methylammonium/methylammonia (14C-MA) was determined. In CO(2)/HCO(3)--free solution, cells at normal pH briefly accumulated 14C-MA over 7 min and reached a plateau. In CO(2)/HCO(3)- solution, however, cells markedly accumulated 14C-MA over the experimental period of 30 min. This CO(2)/HCO(3)--dependent accumulation was reduced by the bicarbonate transporter blocker, 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS; 0.5 mm). Replacing Cl- with gluconate reduced the accumulation, but the reduction was more substantial in the presence of DIDS. Incubation of cells at pH 6.8 (adjusted with NaHCO(3) in 5% CO(2)) for 24 h lowered the mean steady-state intracellular pH to 6.96, significantly lower than 7.28 for control cells. The presence of DIDS reduced 14C-MA accumulation in control conditions but had no effect after acidic incubation. Immunoblotting showed that NBCn1 was upregulated after acidic incubation and in NH(4)Cl-containing media. The Cl--HCO(3)- exchanger AE2 was present, but its expression remained unaffected by acidic incubation. Expressed in Xenopus oocytes, NBCn1 increased carrier-mediated 14C-MA transport, which was abolished by replacing Na+. Two-electrode voltage clamp of oocytes exhibited negligible current after NH(4)Cl application. These results suggest that DIDS-sensitive HCO(3)- extrusion normally governs NH(4)+/NH(3) uptake in the medullary thick ascending limb cells. We propose that, in acidic conditions, DIDS-sensitive HCO(3)- extrusion is inactivated, while NBCn1 is upregulated to stimulate NH(4)+ transport.
Details
- Title: Subtitle
- Sodium-bicarbonate cotransporter NBCn1 in the kidney medullary thick ascending limb cell line is upregulated under acidic conditions and enhances ammonium transport
- Creators
- Soojung Lee - Emory UniversityHye Jeong Lee - Emory UniversityHan Soo Yang - Emory UniversityIan M. Thornell - University of Alabama at BirminghamMark O. Bevensee - University of Alabama at BirminghamInyeong Choi - Emory University
- Resource Type
- Journal article
- Publication Details
- Experimental physiology, Vol.95(9), pp.926-937
- Publisher
- Wiley
- DOI
- 10.1113/expphysiol.2010.053967
- PMID
- 20591978
- PMCID
- PMC2923243
- ISSN
- 0958-0670
- eISSN
- 1469-445X
- Number of pages
- 12
- Grant note
- R01NS046653 / NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA; NIH National Institute of Neurological Disorders & Stroke (NINDS) R01-GM078502; NS046653 / NIH; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA Emory URC KRF-2007-357-C00121 / Korean Government R01GM078502 / NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA; NIH National Institute of General Medical Sciences (NIGMS) National Kidney Foundation
- Language
- English
- Date published
- 09/01/2010
- Academic Unit
- Pulmonary, Critical Care, and Occupational Medicine; Internal Medicine
- Record Identifier
- 9984359697702771
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