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Chloride‐dependent transport of NH 4 + into bee retinal glial cells
Author(s) -
Marcaggi Païkan,
Thwaites David T.,
Deitmer Joachim W.,
Coles Jonathan A.
Publication year - 1999
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.1460-9568.1999.00418.x
Subject(s) - cotransporter , bumetanide , intracellular ph , ammonium chloride , extracellular , chemistry , biophysics , ammonium , intracellular , membrane potential , biochemistry , inorganic chemistry , nuclear chemistry , sodium , biology , organic chemistry
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 NH 4 + /NH 3 . We have studied the entry of NH 4 + /NH 3 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 m m . This acidifying response to ammonium was abolished by the loop diuretic bumetanide (100 μ m ) and by removal of extracellular Cl – . These results strongly suggest that ammonium enters the cell by cotransport of NH 4 + with Cl – . Removal of extracellular Na + did not abolish the NH 4 + ‐induced acidification. The NH 4 + ‐induced pH change was unaffected when nearly all K + conductance was blocked with 5 m m Ba 2+ showing that NH 4 + did not enter through Ba 2+ ‐sensitive ion channels. Application of 2 m m NH 4 + 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 NH 3 , we suggest that when NH 4 + entered the cells, NH 3 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 m m NH 4 + alkalinized the extracellular space: this alkalinization was reduced in the absence of bath Cl – . We conclude that NH 4 + enters the glial cells in bee retina on a cotransporter with functional similarities to the NH 4 + (K + )‐Cl – cotransporter described in kidney cells.