Defining the Physiological Role of the Na, K-ATPase Alpha 1 and Alpha 2 Isoforms in the Regulation of Cardiovascular Function
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| Language: | English |
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University of Cincinnati / OhioLINK
2004
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=ucin1100887954 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-ucin1100887954 |
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NDLTD |
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English |
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Na,K-ATPase &945 1 isoform &945 2 isoform cardiac contrctility vascular tone blood pressure endogenous cardiac glycosides |
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Na,K-ATPase &945 1 isoform &945 2 isoform cardiac contrctility vascular tone blood pressure endogenous cardiac glycosides Dostanic, Ivan Defining the Physiological Role of the Na, K-ATPase Alpha 1 and Alpha 2 Isoforms in the Regulation of Cardiovascular Function |
| author |
Dostanic, Ivan |
| author_facet |
Dostanic, Ivan |
| author_sort |
Dostanic, Ivan |
| title |
Defining the Physiological Role of the Na, K-ATPase Alpha 1 and Alpha 2 Isoforms in the Regulation of Cardiovascular Function |
| title_short |
Defining the Physiological Role of the Na, K-ATPase Alpha 1 and Alpha 2 Isoforms in the Regulation of Cardiovascular Function |
| title_full |
Defining the Physiological Role of the Na, K-ATPase Alpha 1 and Alpha 2 Isoforms in the Regulation of Cardiovascular Function |
| title_fullStr |
Defining the Physiological Role of the Na, K-ATPase Alpha 1 and Alpha 2 Isoforms in the Regulation of Cardiovascular Function |
| title_full_unstemmed |
Defining the Physiological Role of the Na, K-ATPase Alpha 1 and Alpha 2 Isoforms in the Regulation of Cardiovascular Function |
| title_sort |
defining the physiological role of the na, k-atpase alpha 1 and alpha 2 isoforms in the regulation of cardiovascular function |
| publisher |
University of Cincinnati / OhioLINK |
| publishDate |
2004 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1100887954 |
| work_keys_str_mv |
AT dostanicivan definingthephysiologicalroleofthenakatpasealpha1andalpha2isoformsintheregulationofcardiovascularfunction |
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1719432032890650624 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-ucin11008879542021-08-03T06:10:00Z Defining the Physiological Role of the Na, K-ATPase Alpha 1 and Alpha 2 Isoforms in the Regulation of Cardiovascular Function Dostanic, Ivan Na,K-ATPase &945 1 isoform &945 2 isoform cardiac contrctility vascular tone blood pressure endogenous cardiac glycosides Na,K-ATPase is a transmembrane protein that transports three Na+ out of the cell and two K+ in, utilizing ATP hydrolysis as the driving force. The enzyme is composed of two major subunits; α and β. The α subunit is the catalytic subunit of Na,K-ATPase. It binds translocating cations and ATP. The α subunit is also a pharmacological target for cardiac glycosides, that inhibit Na,K-ATPase activity and are used in the treatment of congestive heart failure. There are four isoforms (α1, α2, α3 and α4) of this subunit, each with a distinct tissue distribution and developmental expression, suggestive of differential and tissue specific functional roles. The overall goal of this thesis was to examine the physiological role of the α1 and α2 isoforms of Na,K-ATPase in the regulation of cardiovascular function. While the α1 isoform is ubiquitously expressed, the α2 isoform is specifically expressed in brain, heart, skeletal muscle, vascular smooth muscle and adipose tissue. Previous studies using knock-out mice showed that animals lacking one copy of the α1 or α2 isoform gene exhibit opposite phenotypes. The heart and skeletal muscle from the α2+/- animals, where the α2 isoform levels were reduced by 50%, were hypercontractile while those of the α1+/- animals, in which α1 levels were reduced by 40%, were hypocontractile. To directly determine the role of the α2 isoform, animals expressing a ouabain-resistant α2 isoform were developed and analyzed following administration of ouabain. By comparing the effect of ouabain in these animals to that in wild type mice, which express a ouabain-sensitive α2 isoform, the functional role of the α2 isoform was determined. These studies demonstrated that the α2 isoform is coupled with contractile properties of cardiac and vascular smooth muscle, and it mediates ouabain-induced positive cardiac and vascular inotropy. As cardiac output and vascular resistance regulate normal blood pressure, the physiological role of the α2 isoform in the regulation of blood pressure was analyzed. The α2 isoform mediated both the acute and chronic pressor effects of ouabain. These studies implicate the α2 isoform in short-term and long-term regulation of blood pressure. To address the role of the α1 isoform, animals expressing the ouabain-sensitive α1 isoform and the ouabain-resistant α2 isoform were developed, and analyzed following administration of ouabain. In this way the α1 isoform would be inhibited without altering the activity of the α2 isoform. Inhibition of the α1 isoform increased cardiac contraction and blood pressure. Thus, the α1 isoform mediates ouabain-induced cardiac positive inotropy and pressor effects. These studies demonstrate that both the α1 and α2 isoforms share similar functional roles in the regulation of cardiovascular physiology. However, these analyses do not address whether there are subtle differences in the mechanisms underlining the function of these two α isoforms in heart. It was postulated that the Na,K-ATPase and specially the α2 isoform modulates Ca2+ levels during contraction through functional coupling with Na+/ Ca2+-exchanger. The analysis of the mechanism underlying these functional priorities demonstrated that both α1 and α2 isoforms functionally interact with the Na/Ca-exchanger. Pretreatment with 10 μM KB-R7943, that inhibits the reverse mode of the Na/Ca-exchanger, abolished the cardiotonic effects of ouabain in isolated wild type and the ouabain-sensitive α1 isoform hearts. Also, the immunoprecipitation analyses demonstrated that both the α1 and α2 isoforms co-localize with the Na/Ca-exchanger in the heart. These studies clearly demonstrate that both the α1 and α2 isoforms regulate cardiac contraction by the same mechanism. The present thesis also focused on determining whether endogenous cardiac glycoside-like compounds, which have been observed by many laboratories, play a physiological role. This was accomplished by analyzing whether there is a physiological consequence by the inability of these endogenous compounds to bind their receptor, i.e. α isoforms of Na,K-ATPase. In all the species, the α2 and α3 isoforms exhibit high affinity for cardiac glycosides and they represent putative receptors for the endogenous cardiac glycoside class of compounds. In contrast the α1 isoform is resistant to ouabain in rodents. However, in other species, such as human, the α1 isoform is sensitive to ouabain and could also serve as a receptor for endogenous cardiac glycosides. To determine the role of the cardiac glycoside-binding site of the α2 isoform, we used animals expressing a ouabain-resistant α2 isoform, i.e. those in which the α2 isoform was modified so it does not interact with ouabain. To determine the role of the cardiac glycoside binding site of the α1 isoform we used mice expressing ouabain-sensitive α1 and ouabain-resistant α2 isoforms, i.e. those in which the α1 isoform was modified to be sensitive to ouabain and the α2 isoform was modified to be resistant. Both of these knock-in animals develop and have normal cardiovascular hemodynamics. Thus, under normal conditions the cardiac glycoside binding site of both the α1 and α2 isoforms do not appear to be important. However, endogenous cardiac glycosides occur at very low levels at rest and are elevated during a number of conditions, such as hypertension and congestive heart failure. Thus, we analyzed our gene-targeting mice under conditions known to increase endogenous cardiac glycosides, one of which is ACTH-induced hypertension. Administration of ACTH increased levels of endogenous cardiac glycosides and induced hypertension in wild type mice, i.e. those that express ouabain-resistant α1 and ouabain-sensitive α2 isoform. In contrast, ACTH had no effect on blood pressure in ouabain-resistant α2 mice, but did result in increased levels of endogenous cardiac glycosides. This demonstrates that the cardiac glycoside- binding site of the α2 isoform mediates ACTH-induced hypertension. When the α1 isoform was modified to be ouabain sensitive in ouabain-resistant α2 isoform mice, ACTH induced hypertension. This demonstrates that the cardiac glycoside binding site of the α1 isoform also plays a role in the development of ACTH-induced hypertension. These studies represent a first important insight into the physiological role of the endogenous cardiac glycoside like molecules. 2004 English text University of Cincinnati / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=ucin1100887954 http://rave.ohiolink.edu/etdc/view?acc_num=ucin1100887954 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |