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Chloride-dependent transport of NH4+ into bee retinal glial cells

Lookup NU author(s): Professor David Thwaites

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Abstract

Mammalian astrocytes convert glutamate to glutamine and bee retinal glial cells convert pyruvate to alanine. To maintain such amination reactions these glial cells may take up NH4+/NH3. We have studied the entry of NH4+/NH3 into bundles of glial cells isolated from bee retina by using the fluorescent dye BCECF to measure pH. Ammonium caused intracellular pH to decrease by a saturable process: the rate of change of pH was maximal for an ammonium concentration of about 5 mM. This acidifying response to ammonium was abolished by the loop diuretic bumetanide (100 mu M) and by removal of extracellular Cl-. These results strongly suggest that ammonium enters the cell by cotransport of NH4+ with Cl-. Removal of extracellular Nat did not abolish the NH4+ induced acidification. The NH4+-induced pH change was unaffected when nearly all K+ conductance was blocked with 5 mM Ba2+ showing that NH4+ did not enter through Ba2+-sensitive ion channels. Application of 2 mM NH4+ led to a large increase in total intracellular proton concentration estimated to exceed 13.5 mEq/L. As the cell membrane appeared to be permeable to NH3, we suggest that when NH4+ entered the cells, NH3 left, so that protons were shuttled into the cell. This shuttle, which was strongly dependent on internal and external pH, was quantitatively modelled. In retinal slices, 2 mM NH4+ alkalinized the extracellular space: this alkalinization was reduced in the absence of bath Cl-. We conclude that NH4+ enters the glial cells in bee retina on a cotransporter with functional similarities to the NH4+(K+)-Cl- cotransporter described in kidney cells.


Publication metadata

Author(s): Thwaites DT; Marcaggi P; Deitmer JW; Coles JA

Publication type: Article

Publication status: Published

Journal: European Journal of Neuroscience

Year: 1999

Volume: 11

Issue: 1

Pages: 167-177

Print publication date: 01/01/1999

ISSN (print): 0953-816X

ISSN (electronic): 1460-9568

Publisher: Wiley-Blackwell Publishing Ltd.

URL: http://dx.doi.org/10.1046/j.1460-9568.1999.00418.x

DOI: 10.1046/j.1460-9568.1999.00418.x


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