Plasma membrane transporter that confers resistance to toxic metalloids by mediating extrusion of arsenite (As(III)) and antimonite (Sb(III)) out of cells. Displays low-affinity As(III)/H(+) and Sb(III)/H(+) exchange activity. Vmax for arsenite is approximately 3 times higher than for antimonite. Expression is highly induced by arsenite and antimonite. Leads to sensitivity to antimony, tellurite, cadmium, and phenylarsine oxide. Heterologous expression endows plants with greater arsenic resistance by enhancing arsenite efflux. Reduces arsenic accumulation in rice grains (PubMed:22107880). Does not lower significantly arsenic tissue levels in Arabidopsis (PubMed:22380876). Belongs to the arsenical resistance-3 (ACR3) (TC 2.A.59) family.