Mitochondrial sodium/calcium antiporter that mediates sodium-dependent calcium efflux from mitochondrion, thereby acting as a key regulator of mitochondrion calcium homeostasis. 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. Able to transport Ca2+ in exchange of either Li+ or Na+, explaining how Li+ catalyzes Ca2+ exchange. In contrast to other members of the family its function is independent of K+.
