Imaging signal transduction in living cells with GFP-based probes

Since the cloning and the eterologous expression of the Green Fluorescence Protein (GFP), a number of applications have been reported where protein lo cation within the cell or gene expression is revealed by fluorescent imagin g of living cells. Modified GFPs, however can now be exploited not only as a fluorescent reporter but also as a dynamic marker of intracellular signal ling events, such as fluctuations in the levels of the second messengers Ca 2+ and cAMP, or as a probe for detecting changes in pH in various cell comp artments, These genetically manipulated GFPs allow monitoring of the bioche mistry of the cell in real time and thus offer the possibility to gain a mo re precise view of the functioning of live cells.