The histidine-rich calcium-binding protein (HRCBP) is expressed in the junctional SR, the site of calcium release from the SR. HRCBP is expressed exclusively in muscle tissues and binds calcium with low affinity and high capacity. In addition, HRCBP interacts with triadin, a protein associated with the ryanodine receptor and thought to be involved in calcium release. Its calcium binding properties, localization to the SR, and interaction with triadin suggest that HRCBP is involved in calcium handling by the SR.