Expression of functional Na,K-ATPase isozymes in normal human cardiac biopsies.
In human heart failure, disturbances in Ca2+ homeostasis are well known but the fate of the Na,K-ATPase isoforms (alpha1beta1, alpha2beta1 and alpha3beta1), the receptors for cardiac glycosides, still remains under study. Microsomes have been purified from non-failing human hearts. As judged by the sensitivities of Na,K-ATPase activity to ouabain (IC50 values: 7.0 +/- 2.5 and 81 +/- 11 nM), 3H-ouabain-binding measurements at equilibrium with and without 10 mM K+ and by a biphasic ouabain dissociation process, at least two finctionally active Na,K-ATPase isozymes coexist in normal human hearts. These are demonstrated as a very high- and a high affinity ouabain-binding site. The KD values are 3.6 +/- 1.6 nM and 17 +/- 6 nM, respectively. The two dissociation rate constants are 42 x 10(4) min(-1) and 360 x 10(-4) min(-1). Addition of 10 mM K+ ions shifted the respective KD values for ouabain from 3.6 +/- 1.6 to 20 +/- 5 nM and from 17 +/- 6 nM to 125 +/- 25 nM, respectively. The isozymes involved are identified by comparing these three pharmacological parameters to those of each alpha/beta-isozyme separately expressed in Xenopus oocytes (9). In human heart, the very high affinity site for ouabain is the alpha1beta1 dimer and the high affinity site is alpha2beta1.
Lelievr
L G
LG
Laboratoire de Pharmacologie des Transports Ioniques Membranaires, EA 2381, Université Paris 7, France. lelievre@paris7.jussieu.fr
Crambert
G
G
Allen
P D
PD
D000818:Animals; D001706:Biopsy; D002458:Cell Fractionation; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006333:Heart Failure / Q000503:physiopathology; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology*; D010042:Ouabain / Q000494:pharmacology; D011869:Radioligand Assay; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase