Cloning and characterization of a potassium-dependent sodium/calcium exchanger in Drosophila

Sodium/calcium(-potassium) exchangers (NCX and NCKX) are critical for the r apid extrusion of calcium, which follows the stimulation of a variety of ex citable cells. To further understand the mechanisms of calcium regulation i n signaling, we have cloned a Drosophila sodium/calcium-potassium exchanger , Nckx30C. The overall deduced protein topology for NCKX30C is similar to t hat of mammalian NCKX, having five membrane-spanning domains in the NH, ter minus separated from six at the COOH-terminal end by a large intracellular loop. We show that NCKX30C functions as a potassium-dependent sodium/calciu m exchanger, and is not only expressed in adult neurons as was expected, bu t is also expressed during ventral nerve cord development in the embryo and in larval imaginal discs, Nckx30C is expressed in a dorsal-ventral pattern in the eye-antennal disc in a pattern that is similar to, but broader than that of wingless, suggesting that large fluxes of calcium may be occurring during imaginal disc development. Nckx30C may not only function in the rem oval of calcium and maintenance of calcium homeostasis during signaling in the adult, but may also play a critical role in signaling during developmen t.