May act in low affinity electroneutral exchange of protons for cations such as Na(+) or K(+) across membranes. May also exchange Li(+) and Cs(+) with a lower affinity. H(+)(out) + Na(+)(in) = H(+)(in) + Na(+)(out) H(+)(out) + K(+)(in) = H(+)(in) + K(+)(out) Tonoplast. Expressed at very low levels in roots and shoots. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.