Sperm-specific sodium/hydrogen exchanger involved in intracellular pH regulation of spermatozoa. Required for sperm motility and fertility. Involved in sperm cell hyperactivation, a step needed for sperm motility which is essential late in the preparation of sperm for fertilization. Required for the expression and bicarbonate regulation of the soluble adenylyl cyclase (sAC). Interacts with soluble adenylyl cyclase (sAC). Testis-specific. Specifically present in the principal piece of sperm tail (at protein level). The ion transport-like region is related to the membrane segments of voltage-gated ion channels. Its function is unknown. Mice are normal but males are sterile. Male sterility is due to defects in sperm motility inability to fertilize intact eggs. Moreover, spermatozoa fail to develop the cAMP-dependent protein tyrosine phosphorylation that coincides with the functional maturation occurring upon incubation in capacitating conditions in vitro. cAMP analogs almost completely rescue the motility and infertility phenotypes. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.