Acts in electroneutral exchange of protons for cations such as Na(+) or Li(+) across plasma membrane. Involved in Na(+) and K(+) homeostasis. Required for cytoplasmic Na(+) and Li(+) detoxification by secreting them from the cytoplasm to the extracellular space. Regulates Na(+) content of the xylem sap. H(+)(out) + Na(+)(in) = H(+)(in) + Na(+)(out) H(+)(out) + K(+)(in) = H(+)(in) + K(+)(out) Interacts with CIPK24/SOS2 and CBL4/SOS3. More expressed in roots than in shoots. Mostly localized in parenchyma cells at the xylem/symplast boundary in roots, hypocotyls, stems and leaves. Also present in root tips epidermal cells. By Na(+), in a SOS signaling pathway-dependent manner. Phosphorylated by CIPK24/SOS2 in complex with CBL4/SOS3. Positively regulated by the salt overly sensitive (SOS) signaling pathway that involves the kinase CIPK24/SOS2 and the calcium sensor CBL4/SOS3. Transgenic plants that overexpress NHX7 have enhanced capability to grow on high saline soils. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.