Seems to be involved in regulation of potassium-sodium homeostasis (PubMed:11489190, PubMed:12795699, PubMed:11959905). Functions as a high-affinity sodium transporter, which mediates increased sodium uptake in roots under potassium deficiency and contributes to sodium accumulation and salt toxicity (PubMed:11489190, PubMed:12795699, PubMed:11959905). Involved in nutritional sodium uptake and distribution in potassium-starved roots to allow plant growth (PubMed:17541409, PubMed:30854552). Functions as sodium-potassium cotransporter (PubMed:19482918). Na(+)(in) = Na(+)(out) K(+)(in) + Na(+)(in) = K(+)(out) + Na(+)(out) Measured in yeast strain disrupted for potassium transporters TRK1 and TRK2. Localizes to the plasma membrane. Expressed in cortical and endodermal cells in roots and in vascular bundle regions in leaves (PubMed:17541409). In roots, expressed in epidermis, exodermis, cortex, and sieve elements and companion cells of phloem (PubMed:19482918). In mature leaves, expressed in large highly vacuolated cells of the adaxial epidermis, phloem and xylem (PubMed:19482918). Induced by potassium starvation in roots (PubMed:11489190, PubMed:12795699, PubMed:17541409). Down-regulated by sodium, potassium, rubidium, lithium and cesium (PubMed:11489190, PubMed:12795699). HKT transporters are proposed to contain 4 pore-forming regions enclosed by transmembrane segments with each containing a potassium channel-like selectivity filter motif. Reduced accumulation of sodium in roots and shoots (PubMed:17541409). Reduced growth under low sodium and potassium starvation conditions (PubMed:17541409). Belongs to the TrkH potassium transport family. HKT (TC 2.A.38.3) subfamily.