title: Chloride-dependent transport of NH4+ into bee retinal glial cells.
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 microM) and by removal of extracellular Cl-. These results strongly suggest that ammonium enters the cell by contransport of NH4+ 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 mM Ba2+ showing that NH4+ did not enter through Ba(2+)-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.
authors.affiliation: INSERM U394, IFR8, Institut François Magendie, Bordeaux, France. Paikan.Marcaggi@bordeaux.inserm.fr
authors.forename: P
authors.initials: P
authors.lastname: Marcaggi
authors.forename: D T
authors.initials: DT
authors.lastname: Thwaites
authors.forename: J W
authors.initials: JW
authors.lastname: Deitmer
authors.forename: J A
authors.initials: JA
authors.lastname: Coles
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D001516:Bees; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D002712:Chlorides / Q000493:pharmacokinetics*; D005110:Extracellular Space / Q000378:metabolism; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D008297:Male; D009457:Neuroglia / Q000737:chemistry / Q000378:metabolism; D009924:Organ Culture Techniques; D017956:Photoreceptor Cells, Invertebrate / Q000737:chemistry / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000493:pharmacokinetics*; D012165:Retinal Ganglion Cells / Q000737:chemistry / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism