Development and aldosterone regulation of sodium transport in the chick (Gallus domesticus) allantoic epithelium

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dc.contributor.advisorAtkinson, Nigel (Nigel S.)en
dc.contributor.advisorBittner, George D.en
dc.contributor.advisorSilverthorn, Dee Unglaub, 1948-en
dc.creatorMachart, Jan Meltonen
dc.date.accessioned2011-03-28T14:54:49Zen
dc.date.available2011-03-28T14:54:49Zen
dc.date.issued2001-08en
dc.descriptiontexten
dc.description.abstractThe chick allantoic epithelium, an extraembryonic membrane, encases the waste fluid generated by the kidney. Volume and ionic composition of the allantoic fluid change dramatically over development. The allantoic epithelium has long been established as a sodium (Na+ )-absorbing epithelium; however, the ontogeny and regulation of its transport capabilities had not been examined. I now report that transepithelial voltage and current (“short-circuit” current, Isc) increase about five-fold from day 9 to day 19 of development, with a highly significant surge in Isc magnitude occurring around day 13. Inhibition of the Isc by amiloride (Na+ channel blocker) and ouabain (Na+ /K+ -ATPase inhibitor) shows that greater than 80 percent of the current is carried by Na+ at all times. The active transport of Na+ is reflected in decreasing allantoic Na+ concentration, while plasma Na+ remains approximately the same. Amiloride sensitivity and presence of the aENaC subunit (Western blot) indicate that the Isc is largely mediated through ENaC-like apical Na+ channels, which operate in tandem with basolateral Na+ /K+ -ATPases to maintain cell composition. I also report that chick allantoic epithelium responds to aldosterone, the primary vertebrate regulator of Na+ balance, with an increase in amilorideinhibitable current. The aldosterone-induced response appears to be age-specific, increasing gradually from 9 to 18 days. Although some preparations exhibit a rapid Isc increase beginning within minutes, the response typically begins about 100 minutes after hormone addition, suggesting a predominantly genomic mechanism of action. In all ages examined, Isc at least doubles by 4 hours after initiation of a response, although the percent increase was greatest in 13-14 day membranes. Mineralocorticoid receptors are present (Western blot), and glucocorticoid receptors are assumed present, in allantoic tissue. Experiments with spironolactone (mineralocorticoid antagonist) and dexamethasone (glucocorticoid agonist) failed to definitively demonstrate through which receptor aldosterone preferentially exerts its effect. However, at experimental concentrations or lower, the aldosterone effect is probably predominantly mediated via mineralocorticoid receptors. This aldosterone-responsive surge in current may enhance allantoic water reabsorption, necessary for hydration of the growing embryo. The allantoic epithelium appears to be an excellent epithelial transport model in which to study basic processes of more complex systems.
dc.description.departmentBiological Sciences, School ofen
dc.format.mediumelectronicen
dc.identifier.urihttp://hdl.handle.net/2152/10729en
dc.language.isoengen
dc.rightsCopyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en
dc.rights.restrictionRestricteden
dc.subjectAldosteroneen
dc.subjectNeural tubeen
dc.subjectChickens--Embryosen
dc.titleDevelopment and aldosterone regulation of sodium transport in the chick (Gallus domesticus) allantoic epitheliumen
thesis.degree.departmentBiological Sciences, School ofen
thesis.degree.disciplineZoologyen
thesis.degree.grantorThe University of Texas at Austinen
thesis.degree.levelDoctoralen
thesis.degree.nameDoctor of Philosophyen

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