Table 1. BAPTA- and APTRA-based chelators: Approaches for modifying affinity for Ca2+

Table 1. BAPTA- and APTRA-based chelators: Approaches for modifying affinity for Ca²⁺

Ca²⁺ chelator^a	Wavelength (nm)^b		Ca²⁺ affinity (μM)^c	Mg²⁺ affinity (mM)^c	Comments/reference^d
Electron-withdrawing substituents
	Excitation	Emission
Fura-FF	330/370	510	20	>100	London et al. (1994)
Fluo-5N	491	516	90	>100	Orange and red versions available; Haugland (2002)
Calcium Green-5N	506	532	14	>100	Oregon Green, orange, and red versions available; Haugland (2002)
Sterically modifying groups
Trans-5	NA	NA	6	>100	Ca²⁺ buffer
Cis-5	NA	NA	0.020	4.2	Ca²⁺ buffer
Decreased ligands
Furaptra (Mag-fura)	330/369	510	25	1.9
Mag-indo	350	390/480	35	2.7
Magnesium Green	506	531	6	1.0	Orange and red versions available; Haugland (2002)

^aCa²⁺ buffers and indicators with altered affinity for Ca²⁺ sorted by the method of modification.
^bExcitation and emission maxima for indicators except fura-FF are from Haugland (2002). Two values for excitation or emission refer to the Ca²⁺-bound and Ca²⁺-unbound states for ratiometric indicators. (NA) Not applicable.
^cCa²⁺ and Mg²⁺ affinities measured in 0.1-0.15 M ionic strength, pH 7.0-7.4, 20°C -23°C, except those for fura-FF, are from Haugland (2002).
^dReferences are provided only for indicators not described in the text.