Biosensors for detection of calcium.

Calcium (Ca) is a universal intracellular messenger capable of governing a plethora of different biological functions. Its versatility is guaranteed on the one hand by a cell type-specific Ca signaling toolkit. On the other hand, the fine compartmentalization of changes in Ca concentration ([Ca]) into specific subcellular domains adds a level of complexity, thus generating a variety of signals that can be differentially decoded into specific cellular events. In this context, mitochondrial Ca dynamics plays a central role, by regulating both specific organelle functions (e.g., regulation of substrate oxidation, release of caspase cofactors) and global cellular events (e.g., shaping of cytoplasmic Ca waves). Here we describe a general method for the detection of intramitochondrial [Ca] using bioluminescent and fluorescent genetically-encoded Ca indicators (GECIs). We will discuss the characteristics of different GECIs, as well as their strengths, limitations and applications.