Aquaporins in rat pancreatic interlobular ducts

The aquaporin (AQP) family of water channels is distributed ubiquitously in many epithelia and plays a fundamental role in transmembrane water transport. The aim of this study is to identify the water transport pathway in pancreatic duct cells where most of the HCO-rich fluid originates. Using digital videomicroscopy, we measured the osmotic water permeability (P(f)) of pancreatic duct epithelium by exposing isolated rat interlobular ducts to the hypotonic solution (145 mosM). To identify mRNA and protein of AQPs expressed in duct cells, we conducted RT-PCR analysis and immunohistochemistry of the isolated duct and pancreas. The calculated P(f) (160-230 microm/s) of the isolated ducts was significantly reduced to 16-35 microm/s by 80-90% with either basolateral or luminal applications of HgCl(2). Fluid secretion evoked by secretin was almost completely abolished by a basolateral or luminal application of HgCl(2). A large amount of AQP1 and small amounts of AQP5 transcripts were detected in the isolated duct cells by RT-PCR. AQP1, but not AQP5, immunoreactivity was present in both luminal and basolateral membranes of the interlobular duct cells. Mercury-sensitive water channels are present in both luminal and basolateral membranes of rat pancreatic ducts. AQP1 of the known AQPs appears to be the main water pathway in interlobular ducts.