The function of SLC9A5 (solute carrier family 9 member A5, Ensembl gene identifier ENSG00000135740) is as follows. Plasma membrane Na(+)/H(+) antiporter. Mediates the electroneutral exchange of intracellular H(+) ions for extracellular Na(+) in 1:1 stoichiometry, thus regulating intracellular pH homeostasis, in particular in neural tissues (PubMed:10692428, PubMed:19276089, PubMed:24936055, PubMed:9933641). Acts as a negative regulator of dendritic spine growth (PubMed:21551074). Plays a role in postsynaptic remodeling and signaling (PubMed:21551074, PubMed:24006492). Can also contribute to organellar pH regulation, with consequences for receptor tyrosine kinase trafficking (PubMed:24936055). {ECO:0000269|PubMed:10692428, ECO:0000269|PubMed:19276089, ECO:0000269|PubMed:21551074, ECO:0000269|PubMed:24006492, ECO:0000269|PubMed:24936055, ECO:0000269|PubMed:9933641}.