[Microscopic imaging of calcium ions with genetically encoded calcium indicators]

Calcium is a second messenger that plays a key role in various cellular processes. Monitoring calcium levels is a prerequisite to their understanding. The first calcium indicators for microscopy were the luminescent protein aequorin and chemical probes. These indicators, however, have serious drawbacks, limiting their use in many types of experiments. Cloning of cDNA for the A. victoria GFP and creation of its first spectral variants has initiated the development of fluorescent, genetically encoded calcium indicators (GECI). They are composed of a fluorescent protein and a calcium-binding protein, usually calmodulin. The binding of calcium to the sensory domain of the indicator affects the fluorescent properties of the chromophore, which enables recording of calcium signals as fluorescent light. GECIs have many advantages and are essential for conducting long-term experiments in vivo. This article gives an overview of the currently available GECIs, the history of their development, applications and microscopic imaging systems.