Measurement of cytoplasmic, free magnesium concentration with entrapped eriochrome blue in nerve endings isolated from the guinea pig brain.
Cytoplasmic, free Mg2+ was measured spectrophotometrically using an intrasynaptosomally entrapped Mg2+-indicator, Eriochrome blue (EB). Addition of the ionophore A23187 or disruption of the synaptosomal plasma membrane with digitonin caused an increase in absorbance of entrapped EB with a maximum at 551 nm, which is typical for the Mg2+-EB complex. A conversion of absorbance changes to levels of free Mg2+ concentrations was performed after disruption of synaptosomal plasma membranes by digitonin. The results indicated that the internal, free Mg2+ increased from 0.34 to 2.2 mM when the extracellular Mg2+ concentration was increased from 1 to 5 mM. The low values of cytoplasmic, free Mg2+ concentrations suggest the presence of effective regulatory mechanisms in the nerve endings.
D000818:Animals; D001391:Azo Compounds; D002540:Cerebral Cortex / Q000032:analysis*; D003593:Cytoplasm / Q000032:analysis; D004072:Digitonin / Q000494:pharmacology; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D008274:Magnesium / Q000032:analysis*; D013053:Spectrophotometry; D013574:Synaptosomes / Q000032:analysis
D001391:Azo Compounds; D007202:Indicators and Reagents; C007618:Eriochrome Blue SE; D008274:Magnesium; D004072:Digitonin