Plasma membrane anion exchange protein of wide distribution. Isoform a is widely expressed at similar levels in all tissues examined. Isoforms B1 and B2 are predominantly expressed in stomach although they are also detected at lower levels in other tissues. Isoform C1 is stomach-specific. Isoform C2 is expressed at slightly higher levels in lung and stomach than in other tissues. Belongs to the anion exchanger (TC 2.A.31) family.