Abstract
Plasma membrane Ca^2+^ATPases (PMCAs) export Ca^2+^ from cells in a highly regulated manner, providing fine‐tuning to the maintenance of intracellular Ca^2+^ concentrations. There are few studies of PMCAs in spermatozoa, which is surprising considering the importance of this enzyme in all cell types. Here we describe the primary structure and localization of the PMCA of sea urchin spermatozoa (suPMCA). The suPMCA is 1,154 amino acids and has 56% identity and 76% similarity to all 4 human PMCA isoforms. The suPMCA shares the features of a typical PMCA, including domains for calmodulin binding, ATP binding, ATPase phosphorylation, and 10 putative transmembrane segments with two large cytoplasmic loops. Southern blots show that suPMCA is a single copy gene. Treatment of live sea urchin sperm with the PMCA inhibitor, 5‐(‐6)‐carboxyeosin, results in elevations of intracellular Ca^2+^ and loss of flagellar motility. Immunoblotting and immunoflorescence show that suPMCA is concentrated in the sperm head plasma membrane. In previous work, we showed that a plasma membrane K^+^ dependent Na^+^/Ca^2+^ exchanger (suNCKX), which also keeps Ca^2+^ low in these cells, is concentrated in the sperm flagellum. Thus, the sperm head and flagellum localize different gene products, both functioning to keep intracellular Ca^2+^ low, while the sperm swims in seawater containing 10 mM Ca^2+^. J. Cell. Physiol. 207: 413–419, 2006. © 2005 Wiley‐Liss, Inc.