Postnatal changes in Na,K-ATPase isoform expression in rat cardiac ventricle. Conservation of biphasic ouabain affinity

• Published in: The Journal of biological chemistry 1991-05, Vol.266 (14), p.9327-9331
• Main Authors: LUCCHESI, P. A, SWEADNER, K. J
• Format: Article
• Language: English
• Subjects: Age Factors; Analytical, structural and metabolic biochemistry; Animals; Binding Sites; Biological and medical sciences; Blotting, Western; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; heart; Heart Ventricles - enzymology; Heart Ventricles - growth & development; Hydrolases; Isoenzymes - antagonists & inhibitors; Isoenzymes - immunology; Isoenzymes - metabolism; Na super(+)/K super(+)-transporting ATPase; Ouabain - metabolism; Ouabain - pharmacology; Rats; Sodium-Potassium-Exchanging ATPase - antagonists & inhibitors; Sodium-Potassium-Exchanging ATPase - immunology; Sodium-Potassium-Exchanging ATPase - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)31589-8

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.