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Kennel PJ, Mancini DM, Schulze PC. Skeletal Muscle Changes in Chronic Cardiac Disease and Failure. Compr Physiol 2015; 5:1947-69. [PMID: 26426472 DOI: 10.1002/cphy.c110003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Peak exercise performance in healthy man is limited not only by pulmonary or skeletal muscle function but also by cardiac function. Thus, abnormalities in cardiac function will have a major impact on exercise performance. Many cardiac diseases affect exercise performance and indeed for some cardiac conditions such as atherosclerotic heart disease, exercise testing is frequently used not only to measure functional capacity but also to make a diagnosis of heart disease, evaluate the efficacy of treatment, and predict prognosis. Early in the course of cardiac diseases, exercise performance will be minimally affected but with disease progression impairment in exercise capacity will become apparent. Ejection fraction, that is, the percent of blood volume ejected with each cardiac cycle is often used as a measure of cardiac performance but frequently there is a dissociation between the ejection fraction and exercise capacity in patients with heart disease. How abnormalities in cardiac function impacts the muscles, vasculature, and lungs to impact exercise performance will here be reviewed. The focus of this work will be on patients with systolic heart failure as the incidence and prevalence of heart failure is reaching epidemic proportions and heart failure is the end result of many other chronic cardiac diseases. The prognostic role of exercise and benefits of exercise training will also be discussed.
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Affiliation(s)
- Peter J Kennel
- Center for Advanced Cardiac Care, Division of Cardiology, New York-Presbyterian Hospital and Columbia University Medical Center, New York, USA
| | - Donna M Mancini
- Center for Advanced Cardiac Care, Division of Cardiology, New York-Presbyterian Hospital and Columbia University Medical Center, New York, USA
| | - P Christian Schulze
- Center for Advanced Cardiac Care, Division of Cardiology, New York-Presbyterian Hospital and Columbia University Medical Center, New York, USA
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Moreno AM, Castro RRT, Silva BM, Villacorta H, Sant'Anna Junior M, Nóbrega ACL. Intercostal and forearm muscle deoxygenation during respiratory fatigue in patients with heart failure: potential role of a respiratory muscle metaboreflex. ACTA ACUST UNITED AC 2014. [PMID: 25296359 PMCID: PMC4230287 DOI: 10.1590/1414-431x20143896] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The purpose of this study was to determine the effect of respiratory muscle fatigue
on intercostal and forearm muscle perfusion and oxygenation in patients with heart
failure. Five clinically stable heart failure patients with respiratory muscle
weakness (age, 66±12 years; left ventricle ejection fraction, 34±3%) and nine matched
healthy controls underwent a respiratory muscle fatigue protocol, breathing against a
fixed resistance at 60% of their maximal inspiratory pressure for as long as they
could sustain the predetermined inspiratory pressure. Intercostal and forearm muscle
blood volume and oxygenation were continuously monitored by near-infrared
spectroscopy with transducers placed on the seventh left intercostal space and the
left forearm. Data were compared by two-way ANOVA and Bonferroni correction.
Respiratory fatigue occurred at 5.1±1.3 min in heart failure patients and at 9.3±1.4
min in controls (P<0.05), but perceived effort, changes in heart rate, and in
systolic blood pressure were similar between groups (P>0.05). Respiratory fatigue
in heart failure reduced intercostal and forearm muscle blood volume (P<0.05)
along with decreased tissue oxygenation both in intercostal (heart failure,
-2.6±1.6%; controls, +1.6±0.5%; P<0.05) and in forearm muscles (heart failure,
-4.5±0.5%; controls, +0.5±0.8%; P<0.05). These results suggest that respiratory
fatigue in patients with heart failure causes an oxygen demand/delivery mismatch in
respiratory muscles, probably leading to a reflex reduction in peripheral limb muscle
perfusion, featuring a respiratory metaboreflex.
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Affiliation(s)
- A M Moreno
- Procordis Hospital Cardiológico, Niterói, RJ, Brasil
| | - R R T Castro
- Programa de Pós-graduação em Ciências Cardiovasculares, Universidade Federal Fluminense, Niterói, RJ, Brasil
| | - B M Silva
- Departamento de Fisiologia e Farmacologia, Universidade Federal Fluminense, Niterói, RJ, Brasil
| | - H Villacorta
- Programa de Pós-graduação em Ciências Cardiovasculares, Universidade Federal Fluminense, Niterói, RJ, Brasil
| | | | - A C L Nóbrega
- Departamento de Fisiologia e Farmacologia, Universidade Federal Fluminense, Niterói, RJ, Brasil
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Blain AM, Straub VW. δ-Sarcoglycan-deficient muscular dystrophy: from discovery to therapeutic approaches. Skelet Muscle 2011; 1:13. [PMID: 21798091 PMCID: PMC3156636 DOI: 10.1186/2044-5040-1-13] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Accepted: 03/17/2011] [Indexed: 11/10/2022] Open
Abstract
Mutations in the δ-sarcoglycan gene cause limb-girdle muscular dystrophy 2F (LGMD2F), an autosomal recessive disease that causes progressive weakness and wasting of the proximal limb muscles and often has cardiac involvement. Here we review the clinical implications of LGMD2F and discuss the current understanding of the putative mechanisms underlying its pathogenesis. Preclinical research has benefited enormously from various animal models of δ-sarcoglycan deficiency, which have helped researchers to explore therapeutic approaches for both muscular dystrophy and cardiomyopathy.
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Affiliation(s)
- Alison M Blain
- Institute of Genetic Medicine, Newcastle University, International Centre for Life, Central Parkway, Newcastle upon Tyne, NE1 3BZ, UK
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Coirault C, Hagège A, Chemla D, Fratacci MD, Guérot C, Lecarpentier Y. Angiotensin-converting enzyme inhibitor therapy improves respiratory muscle strength in patients with heart failure. Chest 2001; 119:1755-60. [PMID: 11399702 DOI: 10.1378/chest.119.6.1755] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
STUDY OBJECTIVES Respiratory muscle strength has been shown to be reduced in patients with chronic heart failure. The purpose of this prospective study was to determine whether long-term therapy with the angiotensin-converting enzyme (ACE) inhibitor perindopril improves respiratory muscle strength in patients with chronic heart failure. PATIENTS AND METHODS Eighteen patients with stable chronic heart failure were administered perindopril, 4 mg/d, in addition to their standard therapy for a period of 6 months. Fourteen patients completed the study. Maximum inspiratory pressure (PImax) and maximum expiratory pressure (PEmax) expressed in percentage of predicted values, left ventricular ejection fraction (LVEF) determined by means of two-dimensional echocardiography, and pulmonary volumes were obtained before and after therapy. MEASUREMENTS AND RESULTS As compared to baseline, there was a significant increase in both PImax and PEmax after therapy (57 +/- 27% predicted vs 78 +/- 36% predicted and 62 +/- 20% predicted vs 73 +/- 15% predicted, respectively; each p < 0.05). LVEF increased (34 +/- 5% vs 41 +/- 10%; p < 0.05); functional class improved by > or = 1 New York Heart Association (NYHA) class in five patients. There were no changes in pulmonary volumes. No correlation was found between changes in PImax and PEmax and changes in either LVEF or NYHA functional class. CONCLUSIONS In patients with chronic heart failure, long-term therapy with the ACE inhibitor perindopril improved respiratory muscle strength, as indicated by significant increases in PImax and PEmax.
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Affiliation(s)
- C Coirault
- U451 INSERM, Laboratoire d'Optique Appliquée-ENSTA-Ecole Polytechnique, Palaiseau, France.
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Rousseau E, Proteau S. Functional properties of the native type 3 ryanodine receptor Ca2+-release channel from canine diaphragm. Can J Physiol Pharmacol 2001. [DOI: 10.1139/y00-127] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
mRNA and protein analyses have previously shown that the diaphragm expresses two ryanodine receptor isoforms: RyR1 and RyR3.RyR1 is the main Ca2+-releasing pathway in this muscle type. We now report the conducting, gating, and immunological properties of the native and purified forms of the less abundant RyR3 channel. The conductance of this native Ca2+-release channel was 330 pS in 50 mM/250 mM trans/cis CsCH3SO3. It was activated by Ca2+ concentrations of 1-1000 µM, and did not inactivate at mM concentrations of Ca2+. Both isoforms were purified by either a sucrose density gradient or immunoprecipitation as > 450 kDa proteins on SDS-PAGE. Western blot analysis confirmed the presence of RyR1 and RyR3, which displayed conductances of 740 ± 30 and 800 ± 25 pS, respectively, in 250 mM KCl. We thus provide evidence that one form of the diaphragm SR Ca2+-release channels may be classified as RyR3, with gating properties different from those of the well-characterized RyR1 and RyR2 isoforms.Key words: diaphragm, calcium channel, ryanodine receptors, skeletal muscles, excitation-contraction coupling.
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Abstract
Relaxation is the process by which, after contraction, the muscle actively returns to its initial conditions of length and load. In rhythmically active muscles such as diaphragm, relaxation is of physiological importance because diaphragm must return to a relatively constant resting position at the end of each contraction-relaxation cycle. Rapid and complete relaxation of the diaphragm is likely to play an important role in adaptation to changes in respiratory load and breathing frequency. Regulation of diaphragm relaxation at the molecular and cellular levels involves Ca(2+) removal from the myofilaments, active Ca(2+) pumping by the sarcoplasmic reticulum (SR), and decrease in the number of working cross bridges. The relative contribution of these mechanisms mainly depends on sarcomere length, muscle tension, and the intrinsic contractile function. Increased capacity of SR to take up Ca(2+) can arise from increased density of active SR pumping sites or in slow-twitch fibers from phosphorylation of phospholamban, whereas impaired coupling between ATP hydrolysis and Ca(2+) transport into the SR or intracellular acidosis reduces SR Ca(2+) pump activity. In experimental conditions of decreased contractile performance, slowed, enhanced, or unchanged relaxation rates have been reported in vitro. In vivo, a slowing in the rate of decline of the respiratory pressure is generally considered an early reliable index of respiratory muscle fatigue. Impaired relaxation rate may, in turn, favor mismatch between blood flow and metabolic demand, especially at high breathing frequencies.
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Affiliation(s)
- C Coirault
- Laboratoire d'Optique Appliquée, Ecole Nationale Supérieure des Techniques Avancées, Ecole Polytechnique, Institut National de la Santé et de la Recherche Médicale U 451, Batterie de l'Yvette, 91761 Palaiseau Cedex, France
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Hughes PD, Polkey MI, Harrus ML, Coats AJ, Moxham J, Green M. Diaphragm strength in chronic heart failure. Am J Respir Crit Care Med 1999; 160:529-34. [PMID: 10430724 DOI: 10.1164/ajrccm.160.2.9810081] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Reduced respiratory muscle strength has been reported in chronic heart failure (CHF) in several studies. The data supporting this conclusion come almost exclusively from static inspiratory and expiratory mouth pressure maneuvers (MIP, MEP), which many subjects find difficult to perform. We therefore performed a study using measurements that are less dependent on patient aptitude and also provide specific data on diaphragm strength. In 20 male patients and 15 control subjects we measured MIP and MEP as well as esophageal and transdiaphragmatic pressure during maximal sniffs (Sn Pes, Sn Pdi) and cervical magnetic phrenic nerve stimulation (Tw Pdi). In a subgroup the response to paired phrenic nerve stimulation (pTw Pdi) at interpulse intervals from 10 to 200 ms (5 to 100 Hz) was also determined. As expected, MIP was significantly reduced in the CHF group (CHF, 69.5 cm H(2)O; control, 96.7 cm H(2)O; p = 0.01), but differences were much less marked for Sn Pes (CHF, 95.2 cm H(2)O; control, 104.8 cm H(2)O; p = 0.20) and MEP (CHF, 109.1 cm H(2)O; control, 135.7 cm H(2)O; p = 0.09). Diaphragm strength was significantly reduced (Sn Pdi: CHF, 123.8 cm H(2)O; control 143.5 cm H(2)O; p = 0.04. Tw Pdi: CHF, 21.4 cm H(2)O; control, 28.5 cm H(2)O; p = 0.0005). Paired phrenic nerve stimulation suggested a trend to increased twitch summation at 5 to 20 Hz in CHF, although this did not reach significance. We conclude that mild reduction in diaphragm strength occurs in CHF, possibly because of an increased proportion of slow fibers, but overall strength of the respiratory muscles remains well preserved.
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Affiliation(s)
- P D Hughes
- Department of Cardiology and Respiratory Muscle Laboratory, Royal Brompton Hospital and National Heart and Lung Institute, London, UK
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Kanj NA, Nasser MG, Medawar WA, Al Tayeh AU, Khoury MY, Nassar CF. Reversal of impaired calcium homeostasis in the rat diaphragm subjected to Monocrotaline-induced pulmonary hypertension. Toxicol Lett 1999; 105:177-82. [PMID: 10355538 DOI: 10.1016/s0378-4274(98)00398-1] [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: 11/30/2022]
Abstract
Monocrotaline (MCT) pneumotoxicity is known to alter the structure of pulmonary vascular wall and impairs endothelial cell function resulting in pulmonary hypertension. Its effect on the diaphragm muscle has not yet been elucidated. This study examines the effect of MCT pneumotoxicity on calcium transport in the rat diaphragm. Pulmonary hypertension induced by MCT pneumotoxicity caused a significant increase (P < 0.001) in calcium accumulation in strips isolated from rat diaphragms. Treatment of rats having received MCT with Indapamide reduced calcium uptake by diaphragmatic strips to levels that are not significantly different from the control (P > 0.05). Treatment with Indapamide alone did not elicit any change in calcium accumulation in the diaphragmatic strips. Treatment of the animals with MCT, Indapamide or both did not produce any significant change (P > 0.05) in the cell volume of the diaphragmatic strips. Pulmonary hypertension increased calcium uptake by the muscle cells in the rat diaphragm which may alter diaphragmatic contractility; an effect that was prevented by Indapamide.
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Affiliation(s)
- N A Kanj
- Department of Internal Medicine, American University of Beirut Medical Center, Lebanon
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Peters DG, Mitchell HL, McCune SA, Park S, Williams JH, Kandarian SC. Skeletal muscle sarcoplasmic reticulum Ca(2+)-ATPase gene expression in congestive heart failure. Circ Res 1997; 81:703-10. [PMID: 9351444 DOI: 10.1161/01.res.81.5.703] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Congestive heart failure leads to skeletal muscle abnormalities, one of which is a prolongation of sarcoplasmic reticulum Ca2+ flux. The purpose of this study was to determine whether skeletal muscle of spontaneous hypertensive and heart failure rats have alterations in the expression of the sarcoplasmic (or endoplasmic) reticulum Ca(2+)-ATPase (SERCA) gene. Northern analysis revealed that SERCA1, the predominant skeletal muscle isoform, was decreased by 45%, 43%, and 58% in the tibialis anterior, plantaris, and diaphragm muscles, respectively. Ribonuclease protection assay showed that the decrease was due to the adult isoform, SERCA1a, with minor changes in the alternatively spliced neonatal isoform, SERCA1b. There was no change in SERCA1 mRNA levels in gastrocnemius muscles. No change was found in SERCA2a (cardiac/slow skeletal isoform) mRNA or protein levels or in SERCA2b (smooth muscle isoform), dihydropyridine receptor, or alpha-actin mRNA levels in diaphragm muscle. Northern blot and ribonuclease protection assays showed that SERCA2a decreased 61% in the heart while the alternatively spliced isoform, SERCA2b, decreased 27%. Western analysis of the tibialis anterior, diaphragm, and gastrocnemius muscles showed a decrease in SERCA1 protein levels by 46%, 64%, and 42%, respectively, whereas sarcoplasmic reticulum Ca(2+)-ATPase activity, a functional correlate of SERCA expression, was decreased by 38%, 38%, and 40% in the same muscles, SERCA2 protein expression decreased by 36% in the failing heart. Decreases in both mRNA and protein suggest pretranslational control of SERCA1 expression, whereas the lack of decreased SERCA1 mRNA in gastrocnemius muscle suggests translational regulation. The decreased SERCA1 protein expression in all muscles studied probably contributes to contractile abnormalities related to excitation-contraction coupling function in heart failure.
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Affiliation(s)
- D G Peters
- Boston University, Department of Health Sciences, MA 02215, USA
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Picher M, Decrouy A, Proteau S, Rousseau E. Conducting and voltage-dependent behaviors of the native and purified SR Ca2+-release channels from the canine diaphragm. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1328:243-60. [PMID: 9315621 DOI: 10.1016/s0005-2736(97)00104-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The ryanodine-sensitive Ca2+-release channel of the canine diaphragm sarcoplasmic reticulum (SR) was characterized using biochemical assays and the planar lipid bilayer technique. Diaphragm SR membranes have a [3H]ryanodine-binding capacity (Bmax) of 1.2 pmol/mg protein and a binding affinity (K(D)) of 6.3 nM. The conductance of the native channel was 330 pS in 50 mM/250 mM trans/cis CsCH3SO3 and was reduced to 71 pS by 10 mM Ca2+ trans. The Ca2+-release channel was purified as a 400 kDa protein on SDS-PAGE and displayed a conductance of 715 pS in 200 mM KCl. The native and purified Ca2+ channels were activated by micromolar Ca2+ and ATP and inhibited by Mg2+, ryanodine and ruthenium red. Although diaphragm muscle contraction was shown to depend on extracellular Ca2+ like cardiac muscles, we provide evidence that the diaphragm SR Ca2+-release channel may be classified as a skeletal ryanodine receptor isoform. First, the IC50 for [3H]ryanodine binding was in the same range as estimated for skeletal SR, with 20 nM. Second, the channel was maximally activated by 10-30 microM cytoplasmic Ca2+ and inhibited at higher concentrations. Third, ryanodine binding to the diaphragm SR was less sensitive to Ca2+ than cardiac SR, with EC50, values of 50 and 1 microM, respectively. Finally, Ca2+-release activity and [3H]ryanodine binding capacity of the diaphragm and skeletal SR were similarly more sensitive to Mg2+ than cardiac SR. Together, these results suggest a predominantly skeletal-type of excitation-contraction coupling in the diaphragm.
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Affiliation(s)
- M Picher
- Department of Physiology and Biophysics, Faculty of Medicine, University of Sherbrooke, QC, Canada
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Brasileiro FC, Vargas FS, Kavakama JI, Leite JJ, Cukier A, Préfaut C. High-resolution CT scan in the evaluation of exercise-induced interstitial pulmonary edema in cardiac patients. Chest 1997; 111:1577-82. [PMID: 9187177 DOI: 10.1378/chest.111.6.1577] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
OBJECTIVE To evaluate the onset of exercise-induced interstitial pulmonary edema in cardiac patients by high-resolution CT (HRCT). DESIGN Prospective, normal controlled. PARTICIPANTS Thirty subjects divided into three groups: group 1--10 outpatients with chronic congestive heart failure (CCHF), New York Heart Association (NYHA) class I; group 2--10 outpatients with CCHF, NYHA class II/III; and group 3 (control)--10 normal subjects. METHOD HRCT scans were obtained at rest and 4, 8, 12, 16, and 20 min after progressive treadmill exercise test. RESULTS The following HRCT findings consistent with interstitial edema were significantly different (p<0.05) in group 2 when compared with groups 1 and 3: artery/bronchus ratio > 1 in the upper lobes, peripheral increase in the vascular markings, interlobular septal thickening, and peribronchial "cuffing." These differences were maximal at 12 min after exercise and returned to normal values after 20 min. CONCLUSION Interstitial pulmonary edema was present immediately after exercise in CCHF patients. It may be important in the genesis of dyspnea of these patients.
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Affiliation(s)
- F C Brasileiro
- Instituto do Coracão, Faculty of Medicine, University of São Paulo, Brazil
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Tikunov B, Levine S, Mancini D. Chronic congestive heart failure elicits adaptations of endurance exercise in diaphragmatic muscle. Circulation 1997; 95:910-6. [PMID: 9054750 DOI: 10.1161/01.cir.95.4.910] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
BACKGROUND During rest and exercise, patients with heart failure hyperventilate; therefore, the diaphragm can be viewed as undergoing constant moderate-intensity exercise. Accordingly, we hypothesized that heart failure elicits adaptations in the diaphragm similar to those elicited by endurance exercise in the limb muscles of normal subjects. METHODS AND RESULTS Costal diaphragmatic biopsy samples were obtained from 7 normal subjects (age, 36 +/- 20 years) and 10 patients (age, 50 +/- 6 years; left ventricular ejection fraction, 18 +/- 8%) at the time of transplant or left ventricular assist-device placement. We measured the distribution of myosin heavy chain isoforms I, IIa, and IIb by SDS gel electrophoresis. We also measured the activities of the following enzymes: citrate synthase, a marker of oxidative metabolism; beta-hydroxyacyl-CoA dehydrogenase, a marker of lipolytic metabolism; and lactate dehydrogenase, a marker of glycolytic metabolism. In normal subjects, the distribution of myosin heavy chain isoforms I, IIa, and IIb was 43 +/- 2%, 40 +/- 2%, and 17 +/- 1%, respectively. In contrast, in heart failure subjects, the fiber distribution was 55 +/- 2%, 38 +/- 2%, and 7 +/- 2% for types I, IIa, and IIb, respectively. Therefore, in heart failure, myosin heavy chain I is increased (P < .0001) and myosin heavy chain IIb decreased from normal levels (P < .001). Additionally, citrate synthase activity (normal, 0.33 +/- 0.14; heart failure, 0.54 +/- 0.21 mumol.min-1.mg protein-1; P < .05) and beta-hydroxyacyl-CoA dehydrogenase activity (normal, 0.27 +/- 0.04; heart failure, 0.38 +/- 0.02 mumol.min-1.mg protein-1; P < .05) were greater in heart failure patients than in normal subjects, whereas lactate dehydrogenase activity was significantly less in heart failure patients than in normal subjects (normal, 11.6 +/- 4.6; heart failure,: 4.3 +/- 2.2 mumol.min-1.mg protein-1; P < .01). CONCLUSIONS In the diaphragm in heart failure, there is a shift from fast to slow myosin heavy chain isoforms with an increase in oxidative capacity and a decrease in glycolytic capacity. These diaphragmatic muscle changes are consistent with those elicited by endurance training of the limb muscles in normal subjects.
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Affiliation(s)
- B Tikunov
- Department of Medicine, Columbia Presbyterian Medical Center, New York, NY 10032, USA
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Picher M, Decrouy A, Rousseau E. Conducting and voltage-dependent behaviors of potassium ion channels reconstituted from diaphragm sarcoplasmic reticulum: comparison with the cardiac isoform. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1279:93-103. [PMID: 8624367 DOI: 10.1016/0005-2736(95)00239-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Sarcoplasmic reticulum (SR) K+ channels from canine diaphragm were studied upon fusion of longitudinal and junctional membrane vesicles into planar lipid bilayers (PLB). The large-conductance cation selective channel (gamma(max) = 250 pS; Km = 33 mM) displays long-lasting open events which are much more frequent at positive than at negative voltages. A major subconducting state about 45% of the fully-open state current amplitude was occasionally observed at all voltages. The voltage-dependence of the open probability displays a sigmoid relationship that was fitted by the Boltzmann equation and expressed in terms of thermodynamic parameters, namely the free energy (delta Gi) and the effective gating charge (Zs): delta Gi = 0.27 kcal/mol and Zs = -1.19 in 250 mM potassium gluconate (K-gluconate). Kinetic analyses also confirmed the voltage-dependent gating behavior of this channel, and indicate the implication of at least two open and three closed states. The diaphragm SR K+ channel shares several biophysical properties with the cardiac isoform: g = 180 pS, delta Gi = 0.75 kcal/mol, Zs = -1.45 in 150 mM K-gluconate, and a similar sigmoid P(o)/voltage relationship. Little is known about the regulation of the diaphragm and cardiac SR K+ channels. The conductance and gating of these channels were not influenced by physiological concentrations of Ca2+ (0.1 microM-1 mM) or Mg2+ (0.25-1 mM), as well as by cGMP (25-100 microM), lemakalim (1-100 microM), glyburide (up to 10 microM) or charybdotoxin (45-200 nM), added either to the cis or to the trans chamber. The apparent lack of biochemical or pharmacological modulation of these channels implies that they are not related to any of the well characterized surface membrane K+ channels. On the other hand, their voltage sensitivity strongly suggests that their activity could be modulated by putative changes in SR membrane potential that might occur during calcium fluxes.
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Affiliation(s)
- M Picher
- Department of Physiology and Biophysics, Faculty of Medicine, University of Sherbrooke, Canada
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