Exchangers and Ca2+ signaling

Abstract The Na + /Ca 2+ exchanger (NCX) is a transmembrane protein of the plasma membrane involved in calcium homeostasis. It is a low-affinity, high-capacity electrogenic antiporter that extrudes Ca 2+ against its concentration gradient at the expense of the inward-directed sodium gradient. Two different families of NCX exist, one independent of K + (NCX), the other one, Na + /Ca 2+ (K) exchanger (NCKX), also transports K + together with Ca 2+ in exchange for Na + . The exchanger is especially important in excitable cells, where it is necessary to eject large amounts of Ca 2+ on a regular basis. In mammals, three NCX and six NCKX genes have been described, including several alternative splicing isoforms. NCX and NCKX are also present in non-mammalian vertebrates and in invertebrates. Structural and functional properties, regulation of the proteins, and tissue-specific expression of the different isoforms will be discussed in this chapter.