Role of Pendrin in Acid-base Balance.

Pendrin (SLC26A4) is a Na(+)-independent Cl(-)/HCO(3) (-) exchanger which is expressed in the apical membranes of type B and non-A, non-B intercalated cells within the distal convoluted tubule, the connecting tubule, and the cortical collecting duct. In those segments it mediates HCO(3) (-) secretion and chloride (Cl(-)) absorption. In mice, no renal abnormalities are observed under basal conditions, and individuals with genetic disruption of the pendrin (SLC26A4) gene (Pendred syndrome) have normal acid-base balance. In contrast, there are definite differences under conditions wherein the transporter is stimulated. In animal studies, pendrin (SLC26A4) is upregulated with aldosterone analogues, Cl(-) restriction, and metabolic alkalosis, and is down-regulated with Cl loading and metabolic acidosis, independently. However, the exact role of pendrin in humans has not been established to date, and further examinations are necessary.