I don't think that neither fluo-3 (or even better the upgraded fluo-5) or CTC will do a decent job in those conditions. CTC is able to detect only membrane-BOUND calcium and therefore of little use outside the cell. All the fluos' and the rest of commonly used calcium dyes are optimized to respond BELLOW the milimolar range (altough some still have some response), precisely where magfura starts. The short answer would be, if imaging is not absolutely demanded, use ion sensitive electrodes, they're much more reliable and easy to use in the first place.
Good luck


*********** REPLY SEPARATOR  ***********

On 14-07-1999 at 11:40 Dr Pedro J Camello wrote:

>Hi all,
>I´m trying to determine EXTRAcellular calcium concentration using
>magfura2. During the protocol I need to add vanadate, but this ion
>decreases the fluorescence of mag fura. Does anybody know if some
>other calcium dye is insensitive to vanadate? I was thinkin of fluo-3
>and chlorotetraciclin.
>Thanks
>
>Dr Pedro J Camello
>Dpt Physiology
>Fac Veterinary Sciences
>Univ of Extremadura
>PO Box 643
>10071 Caceres
>SPAIN