title: Intracellular free magnesium in synaptosomes measured with entrapped eriochrome blue.
abstract: The free Mg2+ concentration within synaptosomes has been measured with an entrapped Mg2+ indicator, eriochrome blue. Ionophores gramicidin and A23187 slowly increased the absorbance of the entrapped dye. Calibration of the dye response in a Na+-based medium gave a value around 0.3 mM for the internal free Mg2+ concentration at 1 mM external Mg2+. The replacement of Na+ by choline increased this value to around 0.65 mM. Depolarisation with a high K+ concentration or depletion of intrasynaptosomal ATP with FCCP and iodoacetate did not affect the level of intracellular free Mg2+ concentration. An elevation of the external Ca2+ concentration significantly reduced internal Mg2+ to about 0.1 mM. Ca2+ had no significant effect when Na+ was replaced by choline. The results indicate that the intrasynaptosomal Mg2+ activity is partially regulated by a Na+-Mg2+ exchange mechanism which does not directly require ATP as an energy source.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001391:Azo Compounds; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002540:Cerebral Cortex / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005260:Female; D006096:Gramicidin / Q000494:pharmacology; D006168:Guinea Pigs; D007202:Indicators and Reagents; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D012964:Sodium / Q000494:pharmacology; D013053:Spectrophotometry / Q000379:methods; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D001391:Azo Compounds; D007202:Indicators and Reagents; C007618:Eriochrome Blue SE; D006096:Gramicidin; D000001:Calcimycin; D013779:Tetrodotoxin; D000255:Adenosine Triphosphate; D012964:Sodium; D014700:Verapamil; D008274:Magnesium; D002118:Calcium