May be a carbon dioxide/bicarbonate transporter. Interacts with ap1g1. Acidic motifs (DDEEE) in the C-terminal domain are necessary and sufficient for efficient transport to the contractile vacuole. Does not appear to exhibit a phenotype related to osmoregulation perhaps due to functional redundancy with rhgB. Belongs to the ammonium transporter (TC 2.A.49) family. Rh subfamily.