– Fluo-4 is an analog of Fluo-3 with the two chlorine substituents replaced by fluorines, which results in increased fluorescence excitation at 488 nm that gives higher fluorescence signal. Fluo-4 has its absorption maximum at 494 nm, thus making it excitable by the argon-ion laser. Fluo-4 is essentially nonfluorescent without Ca² present, but the fluorescence increases at least 100 times on Ca² binding. Also, because Fluo-4 binds Ca² more weakly (higher Kd) than do fura-2 and indo-1, it is more useful for measuring high transient Ca² concentration during Ca2 spikes.    Fluo-4, pentapotassium is membrane-impermeant, but can be loaded into cells via microinjection or scrape loading. We also cell a membrane-permeant version, Fluo-4 AM Ester. 

 
• K_d: ~335 nM
 
• &lamba;_{Ex/&lamba;Em (low or high [Ca² ]) = 494nm/516nm}
 
• ε(494 nm) = 82,000 M^-1cm^-1
 
• Orange solid soluble in DMSO and water (pH >6)
 
• Store at 4°C. Protect from light, especially when in solution
 
• C₃₆H_25F2K₅N₂O₁₃
 
• MW: 927.09
 

Handling

Store with desiccant; Protect from light