title: Postnatal changes in Na,K-ATPase isoform expression in rat cardiac ventricle. Conservation of biphasic ouabain affinity.
abstract: The cardiac glycoside sensitivity of the rat heart changes during postnatal maturation and in response to certain pathological conditions. The Na,K-ATPase is thought to be the receptor for cardiac glycosides, and there are three isozymes of its catalytic (alpha) subunit with different cardiac glycoside affinities: alpha 1 (low affinity) and alpha 2 and alpha 3 (high affinity). We examined the developmental expression of the alpha subunit isozymes in rat ventricular membrane preparations by immunoblotting with isozyme-specific antibodies. The alpha 1 isozyme was present throughout all stages of maturation. A developmental switch from alpha 3 to alpha 2 occurred between 14 and 21 days after birth. Measurements of [3H]ouabain binding and inhibition of Na,K-ATPase activity indicated that alpha 2 and alpha 3 should make equivalent contributions to ion pump capacity; in both neonatal natal and adult preparations, ouabain interacted with a single class of high-affinity binding sites (KD = 15 or 40 nM, respectively; Bmax = 4-5 pmol/mg protein), and at low concentrations produced a similar degree of Na,K-ATPase inhibition (25%). The results indicate that the developmental difference in cardiac glycoside sensitivity cannot be explained by quantitative differences in the proportion of high-affinity isozymes of the Na,K-ATPase. The switch from alpha 3 to alpha 2 coincides with other major changes in cardiac electrophysiology and calcium metabolism.
authors.affiliation: Neurosurgical Research, Massachusetts General Hospital, Boston 02114.
authors.forename: P A
authors.initials: PA
authors.lastname: Lucchesi
authors.forename: K J
authors.initials: KJ
authors.lastname: Sweadner
mesh_terms: D000367:Age Factors; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D006352:Heart Ventricles / Q000201:enzymology* / Q000254:growth & development; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D010042:Ouabain / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase