Na(+)/H(+) antiporter that extrudes Na(+) or Li(+) in exchange for external protons across the membrane (PubMed:18508966, PubMed:17988971). Contributes to the regulation of intracellular pH, sodium homeostasis, and cell volume. Plays an important role for insulin secretion and clathrin-mediated endocytosis in beta-cells (PubMed:23720317). Involved in sperm motility and fertility (PubMed:27010853). It is controversial whether SLC9B2 plays a role in osteoclast differentiation (PubMed:17988971) or not (PubMed:20441802, PubMed:22985540). Homodimer. Strong colocalization with LAMP1 and TCIRG1 in osteoclasts (PubMed:20441802). In beta-cells colocalizes with RAB4A and SYP (PubMed:23720317). Localizes to the basolateral membrane of polarized osteoclasts (PubMed:20441802). On the contrary to (PubMed:17988971) not detected at the mitochondrion membrane (PubMed:20441802, PubMed:23720317). Widely expressed (PubMed:18000046, PubMed:18508966, PubMed:17988971). However expression seems to be restricted to specific cell types within individual organs, e.g. osteoclasts in the bone, distal tubules of the kidney or beta-cells of Langerhans islets (PubMed:18508966, PubMed:17988971, PubMed:17698421, PubMed:23720317). In sperm specifically present in the principal piece of sperm tail (at protein level) (PubMed:27010853). Not detectable during the early stages of osteoclast differentiation induced by TNFSF11/RANKL (PubMed:17698421, PubMed:17988971). Up-regulated during the later stages of osteoclast differentiation (PubMed:20441802, PubMed:18508966, PubMed:17698421, PubMed:17988971). Up-regulated in macrophages and blood mononuclear cells treated with TNFSF11/RANKL. No visible phenotype. However males show reduced fertility caused by diminished sperm motility (PubMed:27010853). Deficient mice display a pathological glucose tolerance with impaired insulin secretion but normal peripheral insulin sensitivity (PubMed:23720317). Mutant have normal bone density and their bones are characterized by normal structural parameters (PubMed:20441802, PubMed:22985540). Inhibited by phloretin but not by the classical SLC9A-inhibitor amiloride. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.