Ca²⁺ Measurements in Mammalian Cells with Aequorin-based Probes

Aequorin is a Ca²⁺ sensitive photoprotein suitable to measure intracellular Ca²⁺ transients in mammalian cells. Thanks to recombinant cDNAs expression, aequorin can be specifically targeted to various subcellular compartments, thus allowing an accurate measurement of Ca²⁺ uptake and release of different intracellular organelles. Here, we describe how to use this probe to measure cytosolic Ca²⁺ levels and mitochondrial Ca²⁺ uptake in mammalian cells.