Lookup NU author(s): Professor David Thwaites
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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.
Author(s): Thwaites DT; Marcaggi P; Deitmer JW; Coles JA
Publication type: Article
Publication status: Published
Journal: European Journal of Neuroscience
Print publication date: 01/01/1999
ISSN (print): 0953-816X
ISSN (electronic): 1460-9568
Publisher: Wiley-Blackwell Publishing Ltd.
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