The sodium-calcium exchanger is a membrane protein found in many cell types, including muscle cells of the heart. It plays an important role in regulating intracellular calcium levels. This protein facilitates the transfer of three sodium ions from the cytoplasm to outside of the cell for every two calcium ions that enter, resulting in a net movement of one positive charge into the cell. This exchange mechanism allows cells to maintain correct ion concentrations and pH balance inside and outside its membrane, which is necessary for normal cellular function.

The sodium-calcium exchanger is composed of four subunits with 12 transmembrane segments connected by peptide loops. Each subunit has multiple helices that form an electrically charged pore through which cations can pass between compartments inside and outside the cell. The protein contains two binding sites – one on each side of the membrane – that interact with both sodium and calcium ions as they move across it. As these ions bind to their respective sites, they induce conformational changes in the protein structure that allow for transport of either ion depending on what is being moved out or brought into the cell at any given time.