The enteric nervous system plays an important role in the regulation of electrolyte absorption and secretion by the epithelium lining the gastrointestinal tract. In diseases such as colitis and cholecystitis, dramatic changes in the innervation and neurotransmitter content of submucosal nerves are often associated with chronic inflammation and secretory diarrhea. Attempts to systematically study the neuronal pathways involved in regulation of epithelial cell function and the effects of endogenously released classical neurotransmitters and neuropeptides in tissues such as the small intestine and colon have been difficult for two major reasons. First, these tissues contain multiple cell types that possess different ion transport mechanisms which are either undefined or poorly characterized with respect to receptor and second messenger regulation within the cell. Second, the intrinsic nervous system of these organs possesses a large number of neurons that contain a wide variety of transmitters that modulate, either directly or indirectly, the transport activity of the epithelium. In order to gain a more complete understanding of the role of nerves in the regulation of epithelial cell transport function, the porcine gallbladder was chosen as a model for the intestine since the nervous system of the gallbladder is similar, but less complex than that of the intestine and because the epithelium is more homogenous with respect to cell type and transport function than the small intestine or colon. The overall objective of experiments outlined in this proposal is to understand the cellular mechanisms by which a classical neurotransmitter, norepinephrine (NE) and the neuropeptide, vasoactive intestinal peptide (VIP) regulate Na absorption and Cl secretion across the porcine gallbladder epithelium.
The aims of the project are to 1) analyze the endogenous neurotransmitters, released by electrical depolarization of submucosal nerves, that influence ion transport across the epithelium, 2) identify the cellular mechanism by which VIP stimulates Cl secretion and 3) identify the mechanism by which NE stimulates Na absorption and determine what second messenger system is responsible for mediating its effects on the epithelium, The results of the proposed experiments will enhance our understanding of the neuroregulation of ion transport in the gallbladder and provide important insights into the role of submucosal nerves in the regulation of ion transport in the small intestine and colon. Ultimately, an understanding of the neural control mechanisms of the gallbladder and intestine will lead to the development of new pharmacotherapies that may be useful in the treatment of diseases such as cholecystitis and inflammatory bowel disease.
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