Physiological and pathophysiological investigation of lacrimal and pancreatic ductal epithelial cells

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The investigation of epithelial functions under physiological and pathophysiologycal conditions is essential for the better understanding of their role in the body and their related diseases. We have very limited information about the role of LG ducts in tear secretion. Pancreatic research provided useful tools to study the LG ductal functions and opened new potentials in LG research . Thanks to these tools, in the past decades our knowledge were increasing from the physiology and patophysiology of the exocrine pancreas, although there are still many open questions. One of this questions is the pathomechanism of the biliary AP. Better understanding of the disease may lead to the development of new therapeutical approaches. Therefore this work was aimed to demonstrate the importance of physiological characterisation of epithelial cells and to study their function under pathophysiological conditions. Investigation of lacrimal gland ductal secretion In the first part of this study our AIM was to investigate the osmotic water permeability of LG duct epithelium by means of calculation of filtration permeability and to investigate LG ductal fluid secretion with the following METHODS: Experiments were performed on isolated rabbit LG duct segments maintained in short-term culture. Osmotically determined fluid movement or fluid secretion into the closed intraluminal space of cultured LG interlobular ducts was analyzed using video microscopic technique. Therefore our RESULTS were: • The end of the LG ducts sealed after overnight incubation forming a closed luminal space. • For the calculation of osmotic water permeability, ducts were initially perfused with isotonic HEPES buffered solution, and then with hypotonic HEPES buffered solution. Filtration permeability was calculated from the initial slope of the relative volume increase. • Secretory responses to carbachol or to forskolin stimulation were also investigated. Forskolin stimulation resulted in a rapid and sustained secretory response in both solutions. Forskolin- stimulated fluid secretion was completely inhibited by bumetanide both in HEPES buffered and in HCO3-/CO2 buffered solutions, suggesting the central role NKCC1. • Administration of carbachol initiated a rapid but short secretory response in both HEPES buffered and in HCO3-/CO2 buffered solutions. Atropine completely abolished the carbachol-evoked fluid secretion. CONCLUSIONS from the results: (i) A new method was introduced to investigate LG duct function. (ii) Water permeability of rabbit LG duct epithelium was measured by calculating filtration permeability. (iii) Fluid secretion of LG duct cells induced by carbachol or forskolin was also demonstrated. These results provide calculated values of lacrimal duct osmotic permeability and direct experimental evidence of LG duct fluid secretion.   Effect of acids on pancreatic ductal cells Earlier studies showed that CDCA strongly inhibits pancreatic ductal HCO3- secretion through the destruction of mitochondrial function, which may have significance in the pathomechanism of AP. UDCA is known to protect the mitochondria against hydrophobic bile acids and has ameliorating effect on cell death in heptocytes. Therefore, our AIM was to investigate whether UDCA pretreatment has any effect on CDCA-induced pancreatic ductal injury. To study ductal functions under phatophysiological conditions we used the following METHODS: • Guinea pig intra-interlobular pancreatic ducts were isolated by collagenase digestion. Ducts were treated with UDCA for 5 and 24 h and the effect of CDCA on intracellular Ca2+ concentration ([Ca2+]i), pH (pHi), morphological and functional changes of mitochondria, and the rate of apoptosis were investigated. • AP was induced in rat by retrograde intraductal injection of CDCA (0.5%) and the disease severity of pancreatitis was assessed by measuring standard laboratory and histological parameters. Using in vitro and in vivo approaches our RESULST showed that UDCA pretreatment: • completely prevented the inhibitory effect of CDCA on ductal acid-base transporters, • decreased the rate of CDCA-induced mitochondrial injury and cell death • reduced the severity of experimental AP induced by CDCA. Therefore our CONCLUSION is that these results clearly demonstrate that UDCA: (i) suppresses the CDCA-induced pancreatic ductal injury by reducing apoptosis and mitochondrial damage (ii) reduces the severity of CDCA-induced AP. The protective effect of UDCA against hydrophobic bile acids may represent a novel therapeutical target in the treatment of biliary AP.

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