Use of fluorescent Ca2+ dyes with green fluorescent protein and its variants: problems and solutions

We have studied the degree to which fluorescent Ca2+ indicator dyes, and gr een fluorescent protein and its variants, can be used together. We find tha t the most commonly used fluorescent protein, enhanced green fluorescent pr otein (EGFP), seriously contaminates fura 2 signals. We suggest two alterna tive combinations for which there is no detectable contamination of the Ca2 + indicator signal by the fluorescent protein. Blue fluorescent protein can be used with the Ca2+ indicator Fura Red, EGFP can be used with the Ca2+ i ndicator X-Rhod 1. The use of these combinations will permit the accurate m easurement of Ca2+ signals in cells transfected with fluorescent proteins.