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Sostaric S, Petersen AC, Goodman CA, Gong X, Aw TJ, Brown MJ, Garnham A, Steward CH, Murphy KT, Carey KA, Leppik J, Fraser SF, Cameron-Smith D, Krum H, Snow RJ, McKenna MJ. Oral digoxin effects on exercise performance, K + regulation and skeletal muscle Na + ,K + -ATPase in healthy humans. J Physiol 2022; 600:3749-3774. [PMID: 35837833 PMCID: PMC9541254 DOI: 10.1113/jp283017] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 07/08/2022] [Indexed: 11/30/2022] Open
Abstract
Abstract We investigated whether digoxin lowered muscle Na+,K+‐ATPase (NKA), impaired muscle performance and exacerbated exercise K+ disturbances. Ten healthy adults ingested digoxin (0.25 mg; DIG) or placebo (CON) for 14 days and performed quadriceps strength and fatiguability, finger flexion (FF, 105%peak‐workrate, 3 × 1 min, fourth bout to fatigue) and leg cycling (LC, 10 min at 33% VO2peak and 67% VO2peak, 90% VO2peak to fatigue) trials using a double‐blind, crossover, randomised, counter‐balanced design. Arterial (a) and antecubital venous (v) blood was sampled (FF, LC) and muscle biopsied (LC, rest, 67% VO2peak, fatigue, 3 h after exercise). In DIG, in resting muscle, [3H]‐ouabain binding site content (OB‐Fab) was unchanged; however, bound‐digoxin removal with Digibind revealed total ouabain binding (OB+Fab) increased (8.2%, P = 0.047), indicating 7.6% NKA–digoxin occupancy. Quadriceps muscle strength declined in DIG (−4.3%, P = 0.010) but fatiguability was unchanged. During LC, in DIG (main effects), time to fatigue and [K+]a were unchanged, whilst [K+]v was lower (P = 0.042) and [K+]a‐v greater (P = 0.004) than in CON; with exercise (main effects), muscle OB‐Fab was increased at 67% VO2peak (per wet‐weight, P = 0.005; per protein P = 0.001) and at fatigue (per protein, P = 0.003), whilst [K+]a, [K+]v and [K+]a‐v were each increased at fatigue (P = 0.001). During FF, in DIG (main effects), time to fatigue, [K+]a, [K+]v and [K+]a‐v were unchanged; with exercise (main effects), plasma [K+]a, [K+]v, [K+]a‐v and muscle K+ efflux were all increased at fatigue (P = 0.001). Thus, muscle strength declined, but functional muscle NKA content was preserved during DIG, despite elevated plasma digoxin and muscle NKA–digoxin occupancy, with K+ disturbances and fatiguability unchanged.
![]() Key points The Na+,K+‐ATPase (NKA) is vital in regulating skeletal muscle extracellular potassium concentration ([K+]), excitability and plasma [K+] and thereby also in modulating fatigue during intense contractions.
NKA is inhibited by digoxin, which in cardiac patients lowers muscle functional NKA content ([3H]‐ouabain binding) and exacerbates K+ disturbances during exercise. In healthy adults, we found that digoxin at clinical levels surprisingly did not reduce functional muscle NKA content, whilst digoxin removal by Digibind antibody revealed an ∼8% increased muscle total NKA content. Accordingly, digoxin did not exacerbate arterial plasma [K+] disturbances or worsen fatigue during intense exercise, although quadriceps muscle strength was reduced. Thus, digoxin treatment in healthy participants elevated serum digoxin, but muscle functional NKA content was preserved, whilst K+ disturbances and fatigue with intense exercise were unchanged. This resilience to digoxin NKA inhibition is consistent with the importance of NKA in preserving K+ regulation and muscle function.
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Affiliation(s)
- Simon Sostaric
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Aaron C Petersen
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Craig A Goodman
- Institute for Health and Sport, Victoria University, Melbourne, Australia.,Centre for Muscle Research, Department of Anatomy and Physiology, University of Melbourne, Parkville, Australia
| | - Xiaofei Gong
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Tai-Juan Aw
- Department of Epidemiology and Preventive Medicine, Monash University, Alfred Hospital, Melbourne, Australia
| | - Malcolm J Brown
- Department of Biochemistry and Pharmacology, University of Melbourne, Melbourne, Australia
| | - Andrew Garnham
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Collene H Steward
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Kate T Murphy
- Institute for Health and Sport, Victoria University, Melbourne, Australia.,Centre for Muscle Research, Department of Anatomy and Physiology, University of Melbourne, Parkville, Australia
| | - Kate A Carey
- School of Women's and Children's Health, University of New South Wales, Sydney, Australia
| | - James Leppik
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Steve F Fraser
- Institute of Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Australia
| | - David Cameron-Smith
- Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research, Singapore
| | - Henry Krum
- Department of Epidemiology and Preventive Medicine, Monash University, Alfred Hospital, Melbourne, Australia
| | - Rodney J Snow
- Institute of Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Australia
| | - Michael J McKenna
- Institute for Health and Sport, Victoria University, Melbourne, Australia
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Abstract
Clausen, Torben. Na+-K+ Pump Regulation and Skeletal Muscle Contractility. Physiol Rev 83: 1269-1324, 2003; 10.1152/physrev.00011.2003.—In skeletal muscle, excitation may cause loss of K+, increased extracellular K+ ([K+]o), intracellular Na+ ([Na+]i), and depolarization. Since these events interfere with excitability, the processes of excitation can be self-limiting. During work, therefore, the impending loss of excitability has to be counterbalanced by prompt restoration of Na+-K+ gradients. Since this is the major function of the Na+-K+ pumps, it is crucial that their activity and capacity are adequate. This is achieved in two ways: 1) by acute activation of the Na+-K+ pumps and 2) by long-term regulation of Na+-K+ pump content or capacity. 1) Depending on frequency of stimulation, excitation may activate up to all of the Na+-K+ pumps available within 10 s, causing up to 22-fold increase in Na+ efflux. Activation of the Na+-K+ pumps by hormones is slower and less pronounced. When muscles are inhibited by high [K+]o or low [Na+]o, acute hormone- or excitation-induced activation of the Na+-K+ pumps can restore excitability and contractile force in 10-20 min. Conversely, inhibition of the Na+-K+ pumps by ouabain leads to progressive loss of contractility and endurance. 2) Na+-K+ pump content is upregulated by training, thyroid hormones, insulin, glucocorticoids, and K+ overload. Downregulation is seen during immobilization, K+ deficiency, hypoxia, heart failure, hypothyroidism, starvation, diabetes, alcoholism, myotonic dystrophy, and McArdle disease. Reduced Na+-K+ pump content leads to loss of contractility and endurance, possibly contributing to the fatigue associated with several of these conditions. Increasing excitation-induced Na+ influx by augmenting the open-time or the content of Na+ channels reduces contractile endurance. Excitability and contractility depend on the ratio between passive Na+-K+ leaks and Na+-K+ pump activity, the passive leaks often playing a dominant role. The Na+-K+ pump is a central target for regulation of Na+-K+ distribution and excitability, essential for second-to-second ongoing maintenance of excitability during work.
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Affiliation(s)
- Torben Clausen
- Department of Physiology, University of Aarhus, Arhus, Denmark.
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Edner M, Ponikowski P, Jogestrand T. The effect of digoxin on the serum potassium concentration. Scand J Clin Lab Invest 1993; 53:187-9. [PMID: 8385796 DOI: 10.3109/00365519309088406] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
In recent studies on the influence of muscular and symphatoadrenergic activity on digoxin pharmacokinetics, the serum potassium concentration was found to increase during 2 h of supine rest in digitalized healthy subjects and out-patients. The present study was made in order to find out whether this change in serum potassium concentration is dependent on inhibition of the Na-K-ATPase activity by digitalis treatment. Ten healthy subjects were investigated on two separate occasions: before and after digitalization with digoxin 0.37-0.50 mg daily for 10 days. Serum potassium and digoxin concentrations were analysed before and after 2 h of rest in the sitting position. Without digoxin treatment, no change in serum potassium concentration was seen. During digoxin treatment, the serum potassium concentration increased by 0.19 +/- 0.23 mmol(l)-1 (p < 0.05) during the period of rest. Thus, a digitalis-induced depression of Na-K-ATPase activity seems to be a prerequisite for the described change in serum potassium concentration.
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Affiliation(s)
- M Edner
- Department of Cardiology, Karolinska Hospital, Stockholm, Sweden
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Abstract
Potassium is the principle intracellular ion, and its concentration and gradients greatly influence the electrical activity of excitable membranes. Because anaesthesia is so intimately involved with electrically active cells, potassium concentrations in surgical patients have received considerable attention in diagnostic and therapeutic applications. With the ongoing evolution in the indications for potassium, it is important to review the role of potassium in cellular activity, in storage and regulation, in diseases that alter potassium homeostasis, and in the therapeutic implications of perioperative alterations of potassium concentration. A rational approach to abnormal potassium values and the use of potassium in the operating room is sought, based on a physiological understanding of risks and benefits.
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Affiliation(s)
- J E Tetzlaff
- Department of General Anesthesia, Cleveland Clinic Foundation, Ohio 44195-5001
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Struthers AD, Davies DL, Harland D, Price JS, Brown RA, Quigley C, Brown MJ. Adrenaline causes potassium influx in skeletal muscle and potassium efflux in cardiac muscle in rats: the role of Na/K ATPase. Life Sci 1987; 40:101-8. [PMID: 3025540 DOI: 10.1016/0024-3205(87)90258-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Previous in vitro evidence suggests that adrenaline causes K influx in skeletal muscle by stimulating a ouabain sensitive Na/K ATPase membrane pump. However in rabbits, adrenaline induced hypokalaemia was not significantly altered by pretreatment with digoxin (50 micrograms/kg). Rats were infused with adrenaline or saline after being given a tracer dose of 42KCl. Adrenaline caused a highly significant uptake of 42K in skeletal muscle and a decrease in 42K uptake in ventricle. Rats were also studied after receiving a high dose of digoxin (1.4 mg/kg) which by itself produced a significant increase in plasma K, a decrease in plasma Na and a decreased uptake of 42K in ventricle and lung. These results suggest that adequate widespread Na/K ATPase inhibition had been achieved by this dose of digoxin but despite this, adrenaline still caused hypokalaemia and also still caused significant 42K tissue uptake by skeletal muscle. These results suggest that adrenaline causes K influx by skeletal muscle and K efflux by cardiac tissue. Furthermore, the former mechanism was not inhibited by pretreatment with digoxin.
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Muylle E, Van den Hende C, Nuytten J, Deprez P, Vlaminck K, Oyaert W. Potassium concentration in equine red blood cells: normal values and correlation with potassium levels in plasma. Equine Vet J 1984; 16:447-9. [PMID: 6489306 DOI: 10.1111/j.2042-3306.1984.tb01974.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The concentration of potassium in plasma and in red blood cells was determined in 948 horses. The coefficient of correlation between the two parameters was low. In 436 of these horses, which were clinically healthy, the red blood cell potassium (RBCK+) levels did not fit within a normal distribution curve, but a bimodal distribution was observed with a section point at 90 mmol/litre. In 90 per cent of these normal horses, mean RBCK+ content was 97.5 mmol/litre. In the remaining 10 per cent, mean RBCK+ concentration was 93.8 mmol/litre. A subdivision into a 'low potassium group' and a 'high potassium group' was made. In 10 out of 15 horses in the 'low potassium group', bimonthly sampling over a period of one year showed that RBCK+ content remained low. In the remaining five horses an increase was observed.
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Carlmark B, Bergström J, Ericsson F, Hultman E, Reizenstein P. Intracellular potassium in man. A comparison of in vivo and in vitro measurement techniques. Scand J Clin Lab Invest 1982; 42:245-51. [PMID: 7134809 DOI: 10.1080/00365518209168081] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
In order to evaluate different methods of estimating intracellular content of potassium, determinations of potassium were made in erythrocytes, in muscle biopsy specimens and in the total body. The total body potassium (TBK) was related to body weight (Bwt), lean body mass (LBM), dry LBM, soft fat-free solids (SFFS), total body water (TBW) and calculated intracellular fluid (ICF). Sixty-two healthy subjects and 80 patients with various diseases and therapy known to influence the potassium metabolism were studied. Statistically significant correlations were found between potassium content in muscle biopsies related to fat-free solids and TBK/Bwt (r = +0.56, P less than 0.05), TBK/LBM (r = + 0.58, P less than 0.01), dry LBM (r = + 0.54, P less than 0.05) and TBK/SFFS (r = + 0.68, P less than 0.01). A correlation was found between muscle potassium related to intramuscular water and TBK/TBW (r = + 0.47, P less than 0.05). No correlations were found between EK and TBK/LBM, TBK/dry LBM or TBK/ICF. Between EK and serum potassium a negative correlation (r = -0.31, P less than 0.05) was found in a group of untreated hypertensives. It is concluded that the quotients of TBK (TBK/LBM, TBK/TBW and TBK/SFFS) might be used in the study of intracellular potassium--at least in the study of patient groups.
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