Acts in low affinity electroneutral exchange of protons for cations such as Na(+) or K(+) across membranes. Can also exchange Li(+) and Cs(+) with a lower affinity. Involved in vacuolar ion compartmentalization necessary for cell volume regulation and cytoplasmic Na(+) detoxification. Required during leaves expansion, probably to stimulate epidermal cell expansion. Confers competence to grow in high salinity conditions. H(+)(out) + Na(+)(in) = H(+)(in) + Na(+)(out) H(+)(out) + K(+)(in) = H(+)(in) + K(+)(out) Calcium and pH-dependent interaction with CML18/CAM15 (increases when pH decreases, better at pH 5.5 than at pH 7.5). Tonoplast. Possibly also present in endoplasmic reticulum (ER) and Golgi apparatus. Ubiquitous, with higher levels around vascular tissues and guard cells. Present in flowers, particularly in petals, stamens and anthers (including pollen). Slightly expressed in developing ovaries, strongly expressed in developing embryos and in siliques outer integuments (mostly in base and tips). During first days after germination, mainly localized in roots, including root tips. Later, ubiquitous except in root tips. Induced by NaCl, KCl and sorbitol in a ABA-dependent but SOS signaling-independent manner. Also induced by abscisic acid (ABA). Transgenic plants of agricultural interest (e.g. cotton, Brassica napus) that overexpress NHX1 have enhanced capability to grow on high saline soils. Inhibition of Na(+) transport activity but not of K(+) transport activity is mediated by binding with CML18/CAM15. Inhibited by the diuretic compound amiloride and its analogs ethylisopropyl-amiloride (EIPA), 5-(N-ethyl-N-isopropyl)amiloride (MIA), and benzamil. Also down-regulated by quinine. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.