Ionic selectivity of low-affinity ratiometric calcium indicators: mag-Fura-2, Fura-2FF and BTC

K. L. Hyrc, J. M. Bownik, M. P. Goldberg

Research output: Contribution to journalArticlepeer-review

75 Scopus citations


Accurate measurement of elevated intracellular calcium levels requires indicators with low calcium affinity and high selectivity. We examined fluorescence spectral properties and ionic specificity of three low-affinity, ratiometric indicators structurally related to Fura-2: mag-Fura-2 (furaptra), Fura-2FF, and BTC. The indicators differed in respect to their excitation wavelengths, affinity for Ca2+ (K(d) ~20 μM, 6 μM and 12 μM respectively) and selectivity over Mg2+ (K(d) ~2 mM for mag-Fura-2, > 10 mM for Fura-2FF and BTC). Among the tested indicators, BTC was limited by a modest dynamic range upon Ca2+ binding, susceptibility to photodamage, and sensitivity to alterations in pH. All three indicators bound other metal ions including Zn2+, Cd2+ and Gd3+. Interestingly, only in the case of BTC were spectral differences apparent between Ca2+ and other metal ions. For example, the presence of Zn2+ increased BTC fluorescence 6-fold at the Ca2+ isosbestic point, suggesting that this dye may be used as a fluorescent Zn2+ indicator. Fura-2FF has high specificity, wide dynamic range, and low pH sensitivity, and is an optimal low-affinity Ca2+ indicator for most imaging applications. ETC may be useful if experimental conditions require visible wavelength excitation or sensitivity to other metal ions including Zn2+. (C) 2000 Harcourt Publishers Ltd.

Original languageEnglish
Pages (from-to)75-86
Number of pages12
JournalCell Calcium
Issue number2
StatePublished - Feb 2000


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