Plays an essential role in the regulation of calcium transport at the sarcoplasmic reticulum (SR), which is secondarily required for regular muscle contraction. Interacts with SERCA. Colocalizes with SERCA at the sarcoplasmic reticulum and the diad, a structure composed of a single t-tubule paired with a terminal cisterna of the sarcoplasmic reticulum. Strongly expressed in embryonic and larval somatic muscles and postembryonic heart. SclA and SclB double mutants show arrhythmic cardiac contractions and correspondingly, cardiac cells show irregular action potentials (APs), involving 'double' and occasionally failed APs. Calcium transients in these mutants show higher amplitudes and steeper decay than those in wild type flies. This protein is produced by a bicistronic gene which also produces the SclA protein from a non-overlapping reading frame. Wrong choice of frame.