Sorcin is a highly conserved protein, with 95% homology between hamster and human sorcin sequences. Sorcin has four putative Ca-binding domains, two of which exhibit strong homology to calmodulin “EF hand” motifs. Calcium binding directly to sorcin has been demonstrated by in vitro assays. Sorcin is closely related to members of calpain and sarcoplasmic Ca2+-binding protein subfamilies. Sorcin undergoes calcium-dependent translocation from the cytosol to cellular membranes. Sorcin binds to and modulates ryanodine receptors and is widely distributed including heart and brain tissues. At the subcellular level, sorcin localizes to T-tubule junctions of cardiac sarcoplasmic reticulum.