The function of TUNAR (transmembrane neural differentiation associated intracellular calcium regulator, Ensembl gene identifier ENSG00000250366) is as follows. In neurons, plays a role in the regulation of intracellular Ca(2+), possibly by acting as an activator of ATP2A2/SERCA2, thus increasing the efficiency with which Ca(2+) is removed from the cytoplasm (By similarity). Inhibits differentiation of embryonic stem cells into neurons and inhibits neurite outgrowth, likely as a result of its role in intracellular Ca(2+) regulation (By similarity). In pancreatic beta cells, lowers Ca(2+) levels in the endoplasmic reticulum and enhances glucose-stimulated insulin secretion (PubMed:34513312). {ECO:0000250|UniProtKB:A0A1B0GQX2, ECO:0000269|PubMed:34513312}.