Functions as an electroneutral and bidirectional ammonium transporter. May regulate transepithelial ammonia secretion. Homotrimer. Also detected at the basolateral membrane and in subapical vesicles. Expressed in the forestomach and the fundus of the stomach. Expressed at the level of villous in duodenum, jejunum, ileum and colon. Expressed in kidney by connecting segments and collecting tubules (at protein level). Expressed in testis by seminiferous tubules. N-glycosylated. Belongs to the ammonium transporter (TC 2.A.49) family. Rh subfamily.