Calcium Calcium Calcium is a chemical element with symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The
Calcium imaging dye in all cells or selectively in certain cellular subtypes. GECIs have been used in the studies of neuron, T-cell, cardiomyocyte, etc. Regardless of the type of indicator used the imaging procedure is generally very similar. Isolated cells loaded with an indicator or expressing it in the case of GECI, can be viewed using a fluorescence microscope and captured by a Scientific CMOS (sCMOS) camera or CCD camera. Confocal and two-photon microscopes provide improved sectioning ability so that calcium signals can be resolved in micro domains or (for example) synaptic boutons. Images are analyzed by measuring fluorescence intensity changes for