Operates as a K(+)/H(+) antiporter that controls K(+) acquisition and homeostasis. Predominantly expressed in epidermal and cortical cells of mature roots but also barely detected in leaves. Up-regulated by NaCl, K(+) starvation and abscisic acid (ABA). Induced at acidic external pH. Decreased K(+) content in roots. Could complement the kha1 deletion phenotypes in S.cerevisiae. Belongs to the monovalent cation:proton antiporter 2 (CPA2) transporter (TC 2.A.37) family. CHX (TC 2.A.37.4) subfamily.