Cytosolic Ca2+ has long been known to act as a key second messenger in many intracellular pathways including synaptic transmission, muscle contraction, hormonal secretion, and cell growth and proliferation. The mechanism controlling intracellular Ca2+ level influx, either by the calcium-release-activated Ca2+ channels (CRAC) or from intracellular stores, has become of great interest.Recently, several key players of the store-operated complex have been identified: the Orai family consisting of three members, Orai1-3, and the STIM family, which consists of two members, STIM1 and STIM2.3 Orai1 (also known as CRACM1) acts as the store-operated calcium channel (SOC) and STIM1 as the endoplasmic reticulum Ca2+ sensor.Orai1, Orai2, and Orai3 are all capable of forming store-operated channels.Co-expresssion of Orai2 and STIM1 was shown to produce currents that appear similar but smaller than those produced by co-expression of Orai1 and STIM1.Orai2 transcripts are predominantly expressed in kidney, lung, and spleen, and it appears that Orai2 is the only Orai isoform with multiple transcripts.