Molecular Mechanism of Pancreatic Bicarbonate Secretion

Thanks to recent progress in availability of molecular and functional techniques it became possible to search for the basic molecular and cellular processes that mediate and control and fluid secretion by the pancreatic duct. The coordinated action of various transporters on the luminal and basolateral membranes of polarized epithelial cells mediates the transepithelial transport, which involves absorption in the resting state and secretion in the stimulated state. The overall process of HCO3 secretion can be divided into two steps. First, in the blood enters the ductal epithelial cells across the basolateral membrane either by simple diffusion in the forms of and or by the action of an transporter, a cotranporter (NBC) identified as pNBC1. Subsequently, the cells secrete to the luminal space using at least two exit mechanisms at the luminal membrane. One of the critical transporters needed for all forms of secretion across the luminal membrane is the cystic fibrosis transmembrane conductance regulator (CFTR). In the resting state the pancreatic duct, and probably other secretory epithelia, absorb Interestingly, CFTR also control this mechanism. In this review, we discuss recent progress in understanding epithelial transport, in particular the nature of the luminal transporters and their regulation by CFTR.