Hi Ron,
You may want to check out Nature 1997 vol. 385(16) pg 260-265, for an
intriguing technique. Thats the only thing I can think of off the top
of my head. Are you going to measure the fluxes using flow cytometry or
something else? Seems to me that flow cytometry won't be much help -
though I'm curious to know if thats how you're planning to do this.
There is a company called PTI (Photon Technology International) which
makes all kinds of equipment and dyes for measuring ion fluxes too.
Check out: http://www.pti-nj.com/ Might be useful.
Al Sabirsh