title: Measurement of the cytosolic sodium ion concentration in rat brain synaptosomes by a fluorescence method.
abstract: A method for the measurement of the cytosolic Na+ concentration in intact synaptosomes is described. This method makes use of a pH sensitive dye (BCECF) that can be loaded into the cytosol and a relatively specific ionophore (monensin) that can exchange Na+ for H+ across the synaptosomal membrane. By setting conditions such that there is no electrochemical potential difference for H+ across the membrane (no membrane potential and pHi = pHo), addition of ionophore would induce a H+ flux only if there is a concentration difference for Na+. Thus, when there is no fluorescence change (no cytosolic pH change) extracellular [Na+] equals intrasynaptosomal [Na+]. The intrasynaptosomal [Na+] concentration was determined to be 7 +/- 3 mM (n = 5; mean +/- S.E.). The results obtained with this fluorescence method are compared with estimates obtained by atomic absorption spectrometry. Limitations and applications of the method are discussed.
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism / Q000648:ultrastructure; D001923:Brain Chemistry; D002118:Calcium / Q000494:pharmacology; D003600:Cytosol / Q000032:analysis; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D008985:Monensin; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000032:analysis; D011522:Protons; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000032:analysis* / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013054:Spectrophotometry, Atomic; D013574:Synaptosomes / Q000032:analysis*; D014701:Veratridine / Q000494:pharmacology
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; D007473:Ion Channels; D011522:Protons; D010042:Ouabain; D014701:Veratridine; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D008985:Monensin; D012964:Sodium; D011188:Potassium; D002118:Calcium