Table 19.1 Summary of Molecular Probes fluorescent Ca2+ indicators.

Ca2+ Indicator Water-Soluble Salt * Cell-Permeant Ester † Dextran ‡ Mode § Kd (nM) ** Notes
Bis-fura-2 B6810     Ex 340/380
370
1
BTC B6790 B6791   Ex 400/480
7000
2
Calcium Green-1 C3010MP C3011MP, C3012 C6765, C3713, C3714 Em 530
190
3, 4
Calcium Green-2 C3730 C3732   Em 535
550
3, 5
Calcium Green-5N C3737 C3739   Em 530
14,000
3
Calcium Orange C3013 C3015   Em 575
185
2
Calcium Crimson   C3018   Em 615
185
2
Fluo-3 F1240, F3715 F1241, F1242, F14218, F14242, F23915   Em 525
390
3, 4
Fluo-4 F14200 F14201, F14202, F14217, F23917   Em 520
345
3
Fluo-5F F14221 F14222   Em 520
2300
3
Fluo-4FF F23980 F23981   Em 520
9700
3
Fluo-5N F14203 F14204   Em 520
90,000
3
Fura-2 F1200, F6799 F1201, F1221, F1225, F14185 F3029 Ex 340/380
145
2
Fura-4F F14174 F14175   Ex 340/380
770
2
Fura-6F F14178     Ex 340/380
5300
2
Fura-FF F14180 F14181   Ex 340/380
5500
2
Fura Red F14219 F3020, F3021   Ex 420/480
140
2, 6
Indo-1 I1202 I1203, I1223, I1226   Em 405/485
230
2
Mag-fluo-4 M14205 M14206   Em 520
22,000
3
Mag-fura-2 M1290 M1291, M1292   Ex 340/380
25,000
2
Mag-indo-1   M1295   Em 405/485
35,000
2, 7
Magnesium Green M3733 M3735   Em 530
6000
3
Oregon Green 488 BAPTA-1 O6806 O6807 O6798 Em 520
170
3
Oregon Green 488 BAPTA-2 O6808 O6809   Em 520
580
3, 8
Oregon Green 488 BAPTA-6F O23990     Em 520
3000
3
Oregon Green 488 BAPTA-5N O6812     Em 520
20,000
3
Quin-2 Q23918     Em 495
60
2, 9
Rhod-2 R14220 R1244, R1245MP R34676 †† Em 580
570
3, 10
Rhod-3   R10145   Em 580
570
3
Rhod-FF   R23983   Em 580
19,000
3
Rhod-5N R14207     Em 580
320,000
3
X-rhod-1   X14210   Em 600
700
3
X-rhod-5F X23984 X23985   Em 600
1600
3
* Catalog number(s) for the cell-impermeant salt. † Catalog number(s) for the cell-permeant AM ester. ‡ Catalog number(s) for the dextran conjugates. § Measurement wavelengths, in nm, where Ex = fluorescence excitation and Em = fluorescence emission. Indicators for which a pair of wavelengths are listed have dual-wavelength, ratio-measurement capability. ** Ca2+ dissociation constant, measured in vitro at 22°C in 100 mM KCl, 10 mM MOPS, pH 7.2, unless otherwise noted. Kd values depend on temperature, ionic strength, pH and other factors, and are usually higher in situ. Because indicator dextrans are intrinsically polydisperse and have variable degrees of substitution, these values may vary; lot-specific Kd values are printed on the vial in most cases. †† High-affinity dextran conjugate.

1. Ca2+-dependent fluorescence response similar to fura-2 but ~75% greater molar absorptivity. 2. The AM ester form is fluorescent (a major potential source of error in Ca2+ measurements). 3. The AM ester form is nonfluorescent. 4. Calcium Green-1 is more fluorescent than fluo-3 in both Ca2+-bound and Ca2+-free forms. The magnitude of the Ca2+-dependent fluorescence increase is greater for fluo-3; see Fluorescent Ca2+ Indicators Excited with Visible Light—Section 19.3. 5. Larger Ca2+-dependent fluorescence increase than Calcium Green-1. 6. Can also be used in combination with fluo-3 for dual-wavelength ratio measurements, Ex = 488 nm, Em = 530/670 nm ref. 7. Kd determined in 100 mM KCl, 40 mM HEPES, pH 7.0 at 22°C ref. 8. Larger Ca2+-dependent fluorescence increase than Oregon Green 488 BAPTA-1. 9. Kd determined in 120 mM KCl, 20 mM NaCl, pH 7.05 at 37°C.ref 10. The Kd value for the high-affinity rhod dextran (R34676) is ~780 nM.