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All human Na+-K+-ATPase α-subunit isoforms have a similar affinity for cardiac glycosides

Authors :
Jiangnan Wang
Robert A. Farley
Alicia A. McDonough
Jeffrey B. Velotta
Source :
American Journal of Physiology-Cell Physiology. 281:C1336-C1343
Publication Year :
2001
Publisher :
American Physiological Society, 2001.

Abstract

Three α-subunit isoforms of the sodium pump, which is the receptor for cardiac glycosides, are expressed in human heart. The aim of this study was to determine whether these isoforms have distinct affinities for the cardiac glycoside ouabain. Equilibrium ouabain binding to membranes from a panel of different human tissues and cell lines derived from human tissues was compared by an F statistic to determine whether a single population of binding sites or two populations of sites with different affinities would better fit the data. For all tissues, the single-site model fit the data as well as the two-site model. The mean equilibrium dissociation constant ( Kd) for all samples calculated using the single-site model was 18 ± 6 nM (mean ± SD). No difference in Kdwas found between nonfailing and failing human heart samples, although the maximum number of binding sites in failing heart was only ∼50% of the number of sites in nonfailing heart. Measurement of association rate constants and dissociation rate constants confirmed that the binding affinities of the different human α-isoforms are similar to each other, although calculated Kdvalues were lower than those determined by equilibrium binding. These results indicate both that the affinity of all human α-subunit isoforms for ouabain is similar and that the increased sensitivity of failing human heart to cardiac glycosides is probably due to a reduction in the number of pumps in the heart rather than to a selective inhibition of a subset of pumps with different affinities for the drugs.

Details

ISSN :
15221563 and 03636143
Volume :
281
Database :
OpenAIRE
Journal :
American Journal of Physiology-Cell Physiology
Accession number :
edsair.doi.dedup.....51b629968956416db061db608f6dce24
Full Text :
https://doi.org/10.1152/ajpcell.2001.281.4.c1336