At 09:41 PM 9/30/98 +0200, you wrote:

>Anybody know what happens to the calcium and/or the dye after they have
>bound together and been through a cycle of excitation and emission?  Does
>the dye undergo a physical change (?) which results in the calcium being
>released?   If so, is the dye 'weaker' during the next cycle?

I suppose it depends on which dyes you are talking about. The common ones
like fura/indo/ etc do not change physically (or chemically) there is an
equilibrium between the bound form of the dye,  the unbound dye and free
calcium ions. the amount of bound dye depends on the calcium concentration.
The dye will release its calcium if the free calcium concentration drops.
There should not be any difference after several cycles of excitation except
for changes brought about by the exciting light that will gradually reduce
the amount of active dye
Dr. John Cork,
Calcium Imaging Facility
Department of Anatomy, LSUMC,
1901 Perdido St., New Orleans
LA 70112

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