Biosensors for detection of calcium.

Calcium (Ca2+) 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 Ca2+ signaling toolkit. On the other hand, the fine compartmentalization of changes in Ca2+ concentration ([Ca2+]) 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 Ca2+ 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 Ca2+ waves). Here we describe a general method for the detection of intramitochondrial [Ca2+] using bioluminescent and fluorescent genetically-encoded Ca2+ indicators (GECIs). We will discuss the characteristics of different GECIs, as well as their strengths, limitations and applications.