Mitochondrial sodium/calcium antiporter that mediates sodium- dependent calcium efflux from mitochondrion, by mediating the exchange of 3 sodium ions per 1 calcium ion (PubMed:15060069, PubMed:20018762, PubMed:22829870, PubMed:23056385, PubMed:24898248, PubMed:28130126, PubMed:28219928). Plays a central role in mitochondrial calcium homeostasis by mediating mitochondrial calcium extrusion: calcium efflux is essential for mitochondrial function and cell survival, notably in cardiomyocytes (By similarity). Mitochondrial calcium export is ph-dependent (By similarity). Regulates rates of glucose-dependent insulin secretion in pancreatic beta-cells during the first phase of insulin secretion: acts by mediating efflux of calcium from mitochondrion, thereby affecting cytoplasmic calcium responses (PubMed:23056385). Required for store-operated Ca(2+) entry (SOCE) and Ca(2+) release-activated Ca(2+) (CRAC) channel regulation: sodium transport by SLC8B1 leads to promote calcium-shuttling that modulates mitochondrial redox status, thereby regulating SOCE activity (PubMed:28219928). Involved in B-lymphocyte chemotaxis (By similarity). Able to transport Ca(2+) in exchange of either Li(+) or Na(+), explaining how Li(+) catalyzes Ca(2+) exchange (PubMed:15060069, PubMed:28130126). In contrast to other members of the family its function is independent of K(+) (PubMed:15060069). {ECO:0000250|UniProtKB:Q6AXS0, ECO:0000250|UniProtKB:Q925Q3, ECO:0000269|PubMed:15060069, ECO:0000269|PubMed:20018762, ECO:0000269|PubMed:22829870, ECO:0000269|PubMed:23056385, ECO:0000269|PubMed:24898248, ECO:0000269|PubMed:28219928}. This is the function of Ensembl gene identifier ENSG00000089060 (SLC8B1, solute carrier family 8 member B1).