Regulation of extracellular fluid volume and blood pressure by pendrin.

Na+ is commonly designed as the culprit of salt-sensitive hypertension but several studies suggest that abnormal Cl-transport is in fact the triggering mechanism. This review focuses on the regulation of blood pressure (BP) by pendrin, an apical Cl-/HCO3- exchanger which mediates HCO3- secretion and transcellular Cl-transport in type B intercalated cells (B-ICs) of the distal nephron. Studies in mice showed that it is required not only for acid-base regulation but also for BP regulation as pendrin knock-out mice develop hypotension when submitted to NaCl restriction and are resistant to aldosterone-induced hypertension. Pendrin contributes to these processes by two mechanisms. First, pendrin-mediated Cl-transport is coupled with Na+ reabsorption by the Na+-dependent Cl-/HCO3- exchanger NDCBE to mediate NaCl reabsorption in B-ICs. Second, pendrin activity regulates Na+ reabsorption by the adjacent principal cells, possibly by interaction with the ATP-mediated paracrine signalling recently identified between ICs and principal cells. Interestingly, the water channel AQP5 was recently found to be expressed at the apical side of B-ICs, in the absence of a basolateral water channel, and pendrin and AQP5 membrane expressions are both inhibited by K+ depletion, suggesting that pendrin and AQP5 could cooperate to regulate cell volume, a potent stimulus of ATP release. Copyright (C) 2011 S. Karger AG, Basel