Essential contributions of the α2-Na+/K+-ATPase ouabain binding site to cardiac remodeling

This study investigated the effects of sprint training on muscle Na(+)-K(+)-adenosinetriphosphatase (ATPase) concentration, plasma [K+] regulation, muscle performance, and fatigue during severe intermittent exercise. Six untrained male subjects underwent intensive cycle-sprint training for 7 wk. Muscle biopsies were taken at rest from the vastus lateralis muscle before and after 7 wk of training and were assayed for Na(+)-K(+)-ATPase concentration using vanadate-facilitated [3H]ouabain binding to intact samples. Before and after the training period, subjects performed four maximal 30-s exercise bouts (EB) on a cycle ergometer, each separated by a 4-min recovery. Arterialized venous blood samples were drawn immediately before and after each sprint bout and were analyzed for plasma [K+]. The work output was significantly elevated (11%) across all four EBs after training. The muscle [3H]ouabain binding site concentration was significantly increased (16%) from 333 +/- 19 to 387 +/- 15 (SE) pmol/g wet wt after training but was unchanged in muscle obtained from three control subjects. Plasma [K+] rose by 1–2 mmol/l with each EB and declined rapidly by the end of each recovery period. The increases in plasma [K+] resulting from each EB were significantly lower (19%) after training. The ratios of rise in plasma [K+] relative to work output during each EB were also significantly lower (27%) after training. The increased muscle [3H]ouabain binding site concentration and the reduced ratio of rise in [K+] relative to work output with exercise are both consistent with improved plasma and skeletal muscle K+ regulation after sprint training.

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Effects of testosterone suppression, hindlimb immobilization, and recovery on [3H]ouabain binding site content and Na+, K+-ATPase isoforms in rat soleus muscle

Journal of Applied Physiology ◽

10.1152/japplphysiol.01077.2018 ◽

2020 ◽

Vol 128 (3) ◽

pp. 501-513

Author(s):

Muath M. Altarawneh ◽

Erik D. Hanson ◽

Andrew C. Betik ◽

Aaron C. Petersen ◽

Alan Hayes ◽

...

Keyword(s):

Binding Site ◽

Soleus Muscle ◽

Sham Group ◽

Male Rats ◽

Ouabain Binding ◽

Subsequent Recovery ◽

Sham Surgery ◽

Rat Soleus Muscle ◽

And Function ◽

Muscle Excitability

We investigated the effects of testosterone suppression, hindlimb immobilization, and recovery on skeletal muscle Na+,K+-ATPase (NKA), measured via [3H]ouabain binding site content (OB) and NKA isoform abundances (α1–3, β1–2). Male rats underwent castration or sham surgery plus 7 days of rest, 10 days of unilateral immobilization (cast), and 14 days of recovery, with soleus muscles obtained at each time from cast and noncast legs. Testosterone reduction did not modify OB or NKA isoforms in nonimmobilized control muscles. With sham surgery, OB was lower after immobilization in the cast leg than in both the noncast leg (−26%, P = 0.023) and the nonimmobilized control (−34%, P = 0.001), but OB subsequently recovered. With castration, OB was lower after immobilization in the cast leg than in the nonimmobilized control (−34%, P = 0.001), and remained depressed at recovery (−34%, P = 0.001). NKA isoforms did not differ after immobilization or recovery in the sham group. After castration, α2 in the cast leg was ~60% lower than in the noncast leg ( P = 0.004) and nonimmobilized control ( P = 0.004) and after recovery remained lower than the nonimmobilized control (−42%, P = 0.039). After immobilization, β1 was lower in the cast than the noncast leg (−26%, P = 0.018), with β2 lower in the cast leg than in the noncast leg (−71%, P = 0.004) and nonimmobilized control (−65%, P = 0.012). No differences existed for α1 or α3. Thus, both OB and α2 decreased after immobilization and recovery in the castration group, with α2, β1, and β2 isoform abundances decreased with immobilization compared with the sham group. Therefore, testosterone suppression in rats impaired restoration of immobilization-induced lowered number of functional NKA and α2 isoforms in soleus muscle. NEW & NOTEWORTHY: The Na+,K+-ATPase (NKA) is vital in muscle excitability and function. In rats, immobilization depressed soleus muscle NKA, with declines in [3H]ouabain binding, which was restored after 14 days recovery. After testosterone suppression by castration, immobilization depressed [3H]ouabain binding, depressed α2, β1, and β2 isoforms, and abolished subsequent recovery in [3H]ouabain binding and α2 isoforms. This may have implications for functional recovery for inactive men with lowered testosterone levels, such as in prostate cancer or aging.

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Effects of IGF-I infusion on growth and muscle Na(+)-K+ pump concentration in K(+)-deficient rats

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1993.264.5.e810 ◽

1993 ◽

Vol 264 (5) ◽

pp. E810-E815 ◽

Cited By ~ 1

Author(s):

I. Dorup ◽

A. Flyvbjerg

Keyword(s):

Binding Site ◽

Control Group ◽

Recombinant Human Insulin ◽

Ouabain Binding ◽

Muscle Weight ◽

Igf I ◽

Organ Specific ◽

K Deficiency ◽

Edl Muscle

K(+)-deficient rats and control rats were infused for 14 days with vehicle: acetic acid (AcA) or recombinant human insulin-like growth factor-I (IGF-I, 240 micrograms/day) by osmotic minipumps. IGF-I treatment of K(+)-deficient rats did not result in overall growth of carcass or muscles but in marked selective growth of adrenals (+42%) and spleen (+66%). In control rats, IGF-I induced increased body and muscle weight, tibia length, and thymus weight. K+ deficiency was associated with reduced serum IGF-I but unchanged thyroid status. IGF-I treatment of the K(+)-deficient rats restored serum IGF-I and decreased total 3,5,3'-triiodothyronine. In AcA-treated K(+)-deficient rats [3H]ouabain binding site concentration decreased by 63 and 43% in soleus and extensor digitorum longus (EDL) muscle, respectively, compared with the AcA-treated controls. IGF-I had no effect on the [3H]ouabain binding site concentration in the control group, but in K(+)-deficient rats a significant lowering of 26% was observed in EDL. K+ deficiency causes relative organ-specific resistance to the growth-promoting effects of IGF-I, comparable to the effects seen in protein-restricted rats. Reduced circulating IGF-I is not the only cause of the downregulation of Na(+)-K+ pumps in K+ deficiency, and IGF-I treatment of control animals in vivo has no stimulatory effect on the synthesis of Na(+)-K+ pumps.

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ACTH-induced hypertension is dependent on the ouabain-binding site of the α2-Na+-K+-ATPase subunit

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00183.2008 ◽

2008 ◽

Vol 295 (1) ◽

pp. H273-H280 ◽

Cited By ~ 52

Author(s):

John N. Lorenz ◽

Elizabeth L. Loreaux ◽

Iva Dostanic-Larson ◽

Valerie Lasko ◽

J. Renee Schnetzer ◽

...

Keyword(s):

Binding Site ◽

Systolic Pressure ◽

Cardiac Performance ◽

Differential Sensitivity ◽

Wild Type ◽

Ouabain Binding ◽

Atpase Subunit ◽

Acth Treatment ◽

Induced Hypertension ◽

Tail Cuff

ACTH-induced-hypertension is commonly employed as a model of stress-related hypertension, and despite extensive investigation, the mechanisms underlying elevated blood pressure (BP) are not well understood. We have reported that ACTH treatment increases tail-cuff systolic pressure in wild-type mice but not in mutant mice expressing ouabain-resistant α2-Na+-K+-ATPase subunits (α2R/R mice). Since tail-cuff measurements involve restraint stress, the present study used telemetry to distinguish between an effect of ACTH on resting BP vs. an ACTH-enhanced stress response. We also sought to explore the mechanisms underlying ACTH-induced BP changes in mutant α2R/R mice vs. wild-type mice (ouabain-sensitive α2-Na+-K+-ATPase, α2S/S mice). Baseline BP was not different between the two genotypes, but after 5 days of ACTH treatment, BP increased in α2S/S (104.0 ± 2.6 to 117.7 ± 3.0 mmHg) but not in α2R/R mice (108.2 ± 3.2 to 111.5 ± 4.0 mmHg). To test the hypothesis that ACTH hypertension is related to inhibition of α2-Na+-K+-ATPase on vascular smooth muscle by endogenous cardiotonic steroids, we measured BP and regional blood flow. Results suggest a differential sensitivity of renal, mesenteric, and cerebral circulations to ACTH and that the response depends on the ouabain sensitivity of the α2-Na+-K+-ATPase. Baseline cardiac performance was elevated in α2S/S but not α2R/R mice. Overall, the data establish that the α2-Na+-K+-ATPase ouabain-binding site is of central importance in the development of ACTH-induced hypertension. The mechanism appears to be related to alterations in cardiac performance, and perhaps vascular tone in specific circulations, presumably caused by elevated levels of circulating cardiotonic steroids.

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Marinobufagenin enhances cardiac contractility in mice with ouabain-sensitive α1 Na+-K+-ATPase

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00285.2009 ◽

2009 ◽

Vol 296 (6) ◽

pp. H1833-H1839 ◽

Cited By ~ 21

Author(s):

Arshani N. Wansapura ◽

Valerie Lasko ◽

Zijian Xie ◽

Olga V. Fedorova ◽

Alexei Y. Bagrov ◽

...

Keyword(s):

Binding Site ◽

Functional Role ◽

Cardiac Contractility ◽

Cardiac Performance ◽

Wild Type ◽

Ouabain Binding ◽

Atpase Subunit ◽

Cardiac Inotropy ◽

Rats And Mice

Endogenous Na+ pump inhibitors are thought to play important (patho)physiological roles and occur in two different chemical forms in the mammalian circulation: cardenolides, such as ouabain, and bufadienolides, such as marinobufagenin (MBG). Although all α Na+-K+-ATPase isoforms (α1-4) are sensitive to ouabain in most species, in rats and mice the ubiquitously expressed α1 Na+-K+-ATPase is resistant to ouabain. We have previously shown that selective modification of the putative ouabain binding site of either the α1 or α2 Na+-K+-ATPase subunit in mice substantially alters the cardiotonic influence of exogenously applied cardenolides. To determine whether the ouabain binding site also interacts with MBG and if this interaction plays a functional role, we evaluated cardiovascular function in α1-resistant/α2-resistant (α1R/Rα2R/R), α1-sensitive/α2-resistant (α1S/Sα2R/R), and α1-resistant/α2-sensitive mice (α1R/Rα2S/S, wild type). Cardiovascular indexes were evaluated in vivo by cardiac catheterization at baseline and during graded infusions of MBG. There were no differences in baseline measurements of targeted mice, indicating normal hemodynamics and cardiac function. MBG at 0.025, 0.05, and 0.1 nmol·min−1·g body wt−1 significantly increased cardiac performance to a greater extent in α1S/Sα2R/R compared with α1R/Rα2R/R and wild-type mice. The increase in LVdP/d tmax in α1S/Sα2R/R mice was greater at higher concentrations of MBG compared with both α1R/Rα2R/R and α1R/Rα2S/S mice ( P < 0.05). These results suggest that MBG interacts with the ouabain binding site of the α1 Na+-K+-ATPase subunit and can thereby influence cardiac inotropy.

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K+ supplementation increases muscle [Na+-K+-ATPase] and improves extrarenal K+homeostasis in rats

Journal of Applied Physiology ◽

10.1152/jappl.1997.82.4.1136 ◽

1997 ◽

Vol 82 (4) ◽

pp. 1136-1144 ◽

Cited By ~ 20

Author(s):

Henning Bundgaard ◽

Thomas A. Schmidt ◽

Jim S. Larsen ◽

Keld Kjeldsen

Keyword(s):

Binding Site ◽

Phosphatase Activity ◽

Skeletal Muscles ◽

Gastrocnemius Muscle ◽

Matched Control ◽

Lower Plasma ◽

Ouabain Binding ◽

Activity Measurements ◽

Arterial Plasma

Bundgaard, Henning, Thomas A. Schmidt, Jim S. Larsen, and Keld Kjeldsen. K+supplementation increases muscle [Na+-K+-ATPase] and improves extrarenal K+homeostasis in rats. J. Appl. Physiol.82(4): 1136–1144, 1997.—Effects of K+ supplementation (∼200 mmol KCl/100 g chow) on plasma K+, K+ content, and Na+-K+-adeonsinetriphosphatase (ATPase) concentration ([Na+-K+-ATPase]) in skeletal muscles as well as on extrarenal K+ clearance were evaluated in rats. After 2 days of K+supplementation, hyperkalemia prevailed (K+-supplemented vs. weight-matched control animals) [5.1 ± 0.2 (SE) vs. 3.2 ± 0.1 mmol/l, P < 0.05, n = 5–6], and after 4 days a significant increase in K+content was observed in gastrocnemius muscle (104 ± 2 vs. 97 ± 1 μmol/g wet wt, P < 0.05, n = 5–6). After 7 days of K+ supplementation, a significant increase in [3H]ouabain binding site concentration (344 ± 5 vs. 239 ± 8 pmol/g wet wt, P < 0.05, n = 4) was observed in gastrocnemius muscle. After 2 wk, increases in plasma K+, K+ content, and [3H]ouabain binding site concentration in gastrocnemius muscle amounted to 40, 8, and 68% ( P < 0.05) above values observed in weight-matched control animals, respectively. The latter change was confirmed by K+-dependent p-nitrophenyl phosphatase activity measurements. Fasting for 1 day reduced plasma K+ and K+ content in gastrocnemius muscle in rats that had been K+supplemented for 2 wk by 3.1 ± 0.3 mmol/l ( P < 0.05, n = 5) and 15 ± 2 μmol/g wet wt ( P < 0.05, n = 5), respectively. After induction of anesthesia, arterial plasma K+was measured during intravenous KCl infusion (0.75 mmol KCl ⋅ 100 g body wt−1 ⋅ h−1). The K+-supplemented fasted group demonstrated a 42% ( P < 0.05) lower plasma K+ rise, associated with a significantly higher increase in K+ content in gastrocnemius muscle of 7 μmol/g wet wt ( P < 0.05, n = 5) compared with their control animals. In conclusion, K+supplementation increases plasma K+, K+ content, and [Na+-K+-ATPase] in skeletal muscles and improves extrarenal K+ clearance capacity.

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