Fluorescent indicators for cytosolic sodium.
Fluorescent indicators sensitive to cytosolic concentrations of free Na+ have been synthesized and characterized. They consist of a crown ether, 1,7-diaza-4,10,13-trioxacyclopentadecane, linked via its nitrogens to fluorophores bearing additional liganding centers. In the currently preferred dye, SBFI (short for sodium-binding benzofuran isophthalate), the fluorophores are benzofurans linked to isophthalate groups. Selectivities for Na+ over K+ of about 20 are observed, resulting in effective dissociation constants for Na+ of about 20 mM against a background of 120 mM K+. Increasing [Na+] increases the ratio of excitation efficiency at 330-345 nm to that at 370-390 nm with emission collected at 450-550 nm, so that ratio fluorometry and imaging can be performed with the same wavelengths as used with the well known Ca2+ indicator fura-2. If the macrocyclic ring is increased in size to a 1,10-diaza-4,7,13,16-tetraoxacyclooctadecane, the chelators become selective for K+ over Na+.
Minta
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Department of Physiology-Anatomy, University of California, Berkeley 94720.
Tsien
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D003600:Cytosol / Q000378:metabolism*; D015195:Drug Design; D005456:Fluorescent Dyes / Q000138:chemical synthesis*; D007202:Indicators and Reagents; D015394:Molecular Structure; D012964:Sodium / Q000032:analysis*; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship
D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D012964:Sodium