Article: article from journal or magazin.
Transport and pharmacological properties of nine different human Na, K-ATPase isozymes.
Journal of Biological Chemistry
Publication types: Comparative Study ; Journal Article
Na,K-ATPase plays a crucial role in cellular ion homeostasis and is the pharmacological receptor for digitalis in man. Nine different human Na,K-ATPase isozymes, composed of 3 alpha and beta isoforms, were expressed in Xenopus oocytes and were analyzed for their transport and pharmacological properties. According to ouabain binding and K(+)-activated pump current measurements, all human isozymes are functional but differ in their turnover rates depending on the alpha isoform. On the other hand, variations in external K(+) activation are determined by a cooperative interaction mechanism between alpha and beta isoforms with alpha2-beta2 complexes having the lowest apparent K(+) affinity. alpha Isoforms influence the apparent internal Na(+) affinity in the order alpha1 > alpha2 > alpha3 and the voltage dependence in the order alpha2 > alpha1 > alpha3. All human Na,K-ATPase isozymes have a similar, high affinity for ouabain. However, alpha2-beta isozymes exhibit more rapid ouabain association as well as dissociation rate constants than alpha1-beta and alpha3-beta isozymes. Finally, isoform-specific differences exist in the K(+)/ouabain antagonism which may protect alpha1 but not alpha2 or alpha3 from digitalis inhibition at physiological K(+) levels. In conclusion, our study reveals several new functional characteristics of human Na,K-ATPase isozymes which help to better understand their role in ion homeostasis in different tissues and in digitalis action and toxicity.
Animals, Binding, Competitive, Biological Transport, Cell Membrane/enzymology, Cloning, Molecular, Dose-Response Relationship, Drug, Electrophysiology, Enzyme Activation/drug effects, Humans, Isoenzymes, Kinetics, Oocytes/metabolism, Ouabain/antagonists & inhibitors, Ouabain/metabolism, Potassium/pharmacology, RNA, Complementary/metabolism, Sodium/pharmacology, Sodium-Potassium-Exchanging ATPase/genetics, Sodium-Potassium-Exchanging ATPase/metabolism, Xenopus/metabolism
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