The function of SLC9A8 (solute carrier family 9 member A8, ENSG00000197818) is as follows. Na(+)/H(+) antiporter. Mediates the electoneutral exchange of intracellular H(+) ions for extracellular Na(+) in 1:1 stoichiometry (PubMed:15522866). Acts as an Na(+)/H(+) exchanger in the trans-Golgi. Contributes to the regulation of pH regulation of Golgi apparatus, and consequently, in protein trafficking and endosomal morphology (PubMed:15522866, PubMed:20719963). In germ cells, plays a crucial role in acrosome biogenesis and sperm development, probably by playing a role in the fusion of the Golgi-derived vesicles that form the acrosomal cap (By similarity). Can also be active at the cell surface of specialized cells. In the small intestine, at the cell membrane, plays a major physiological role in transepithelial absorption of Na(+) and regulates intracellular pH homeostasis of intestinal epithelial cells (PubMed:34288721). Acts as an important regulator of mucosal integrity in the intestine and in the stomach, could mediate the pH fluctuation necessary for mucin exocytosis or assist membrane trafficking of other proteins (By similarity). Plays a role in photoreceptor survival and in the maintenance of intracellular pH homeostasis in retinal pigment epithelium (RPE cells) (By similarity). {ECO:0000250|UniProtKB:Q8R4D1, ECO:0000269|PubMed:15522866, ECO:0000269|PubMed:20719963, ECO:0000269|PubMed:34288721}.