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The only effect I could envision (and it would not be a strong one) would be
via the contribution of Cl- to the total ionic strength of the solution.  For
BAPTA-based indicators such as fluo-4, the calcium binding affinity decreases
as ionic strength increases (see Biochim Biophys Acta 925, 133 (1987) for data
pertaining to BAPTA).  Affinity constants for indicators cited in the
Molecular Probes handbook are usually measured for  I=0.1 (100 mM KCl).

Ricardo Scott wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> Does anybody have any idea about the next:
>
> Changes in the amount of  Cl- ions could interfere with fluo-4 (or related
> dyes).
>
> Is that true?
> Why is it?
> Any reference about that?
>
> Thanks
>
> Dr Ricardo Scott
> Room 826
> Queen Square
> Institute of Neurology
> University College London
> WC1N 3BG  LONDON  UK