The regulation of intestinal bicarbonate secretion by marine teleost fish

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The regulation of intestinal bicarbonate secretion by marine teleost fish

Show simple item record Whittamore, Jonathan Mark en_GB 2008-12-12T11:34:36Z en_GB 2011-01-25T17:25:53Z en_US 2013-03-21T12:59:51Z 2008-08-28 en_GB
dc.description.abstract In seawater, drinking is a fundamental part of the osmoregulatory strategy for teleost fish, and presents a unique challenge. The intestine has an established role in osmoregulation, and its ability to effectively absorb fluid from imbibed seawater is crucial to compensating for water losses to the surrounding hyperosmotic environment. Alongside solute-linked water transport (driven by NaCl cotransport), intestinal bicarbonate (HCO3-) secretion also benefits fluid absorption directly (via apical Cl-/HCO3- exchange), and indirectly through the formation of calcium carbonate (CaCO3) thus removing the osmotic influence of Ca2+ within the gut fluid. For the European flounder (Platichthys flesus), elevated luminal Ca2+ has proven to be a specific, potent stimulator of HCO3- secretion both in vitro and in vivo where these actions are presumably modulated by an extracellular Ca2+-sensing receptor (CaR). The focus of this work was to learn more about how intestinal HCO3- secretion is regulated, the role of Ca2+, and more specifically the CaR. To achieve this, in vitro ‘gut sac’ experiments investigated how luminal Ca2+ influenced HCO3- secretion, and associated ion and fluid transport. Contrary to expectation, increasing Ca2+ from 5 to 20 mM did not stimulate HCO3- secretion. In an attempt to elucidate the role of CaCO3 precipitation in fluid absorption, and further explore the physiological implications of HCO3- secretion, the intestine was perfused in vivo with salines containing varying concentrations of Ca2+ (10, 40 and 90 mM). The production and secretion of HCO3-, in addition to CaCO3 formation increased accordingly with Ca2+, and was associated with a dramatic 25 % rise in the fraction of fluid absorbed by the gut. Additional in vitro experiments, utilising the Ussing chamber, helped establish some of the characteristics of intestinal HCO3- secretion by the euryhaline killifish (Fundulus heteroclitus), but was unresponsive to elevated mucosal Ca2+. Further attempts to potentiate the activity of the CaR, and application of the receptor agonists gadolinium (Gd3+) and neomycin, failed to produce responses consistent with the effect of Ca2+ observed previously, either in vitro or in vivo. With no evidence supporting a direct role for an extracellular, intestinal CaR in HCO3- secretion it was argued that secretion would be principally regulated by two factors, the ability of the epithelia to generate high levels of intracellular HCO3- and the rate of CaCO3 formation. en_GB
dc.description.sponsorship BBSRC en_GB
dc.identifier.grantnumber BBS/S/A/2004/11078 en_GB
dc.identifier.uri en_GB
dc.language.iso en en_GB
dc.publisher University of Exeter en_GB
dc.subject bicarbonate secretion en_GB
dc.subject osmoregulation en_GB
dc.subject calcium-sensing receptor en_GB
dc.subject chloride-bicarbonate exchange en_GB
dc.subject teleost fish en_GB
dc.subject carbonate precipitation en_GB
dc.subject water transport en_GB
dc.subject calcium en_GB
dc.subject in vitro en_GB
dc.subject in vivo en_GB
dc.title The regulation of intestinal bicarbonate secretion by marine teleost fish en_GB
dc.type Thesis or dissertation en_GB 2008-12-12T11:34:36Z en_GB 2011-01-25T17:25:53Z en_US 2013-03-21T12:59:51Z
dc.contributor.advisor Wilson, Roderic William en_GB
dc.publisher.department School of Biosciences en_GB
dc.type.degreetitle PhD in Biological Sciences en_GB
dc.type.qualificationlevel Doctoral en_GB
dc.type.qualificationname PhD en_GB

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