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 brain, testis, placenta, pancreas, esophagus and prostate. Expressed in squamous epithelial tissues (at protein level). According to PubMed:11062476, specifically expressed in kidney. Specifically expressed in fetal kidney. N-glycosylated. Belongs to the ammonium transporter (TC 2.A.49) family. Rh subfamily.