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Bartlett MF, Fitzgerald LF, Nagarajan R, Kent JA. Measurements of in vivo skeletal muscle oxidative capacity are lower following sustained isometric compared with dynamic contractions. Appl Physiol Nutr Metab 2024; 49:250-264. [PMID: 37906958 DOI: 10.1139/apnm-2023-0315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2023]
Abstract
Human skeletal muscle oxidative capacity can be quantified non-invasively using 31-phosphorus magnetic resonance spectroscopy (31P-MRS) to measure the rate constant of phosphocreatine (PCr) recovery (kPCr) following contractions. In the quadricep muscles, several studies have quantified kPCr following 24-30 s of sustained maximal voluntary isometric contraction (MVIC). This approach has the advantage of simplicity but is potentially problematic because sustained MVICs inhibit perfusion, which may limit muscle oxygen availability or increase the intracellular metabolic perturbation, and thus affect kPCr. Alternatively, dynamic contractions allow reperfusion between contractions, which may avoid limitations in oxygen delivery. To determine whether dynamic contraction protocols elicit greater kPCr than sustained MVIC protocols, we used a cross-sectional design to compare quadriceps kPCr in 22 young and 11 older healthy adults following 24 s of maximal voluntary: (1) sustained MVIC and (2) dynamic (MVDC; 120°·s-1, 1 every 2 s) contractions. Muscle kPCr was ∼20% lower following the MVIC protocol compared with the MVDC protocol (p ≤ 0.001), though this was less evident in older adults (p = 0.073). Changes in skeletal muscle pH (p ≤ 0.001) and PME accumulation (p ≤ 0.001) were greater following the sustained MVIC protocol, and pH (p ≤ 0.001) and PME (p ≤ 0.001) recovery were slower. These results demonstrate that (i) a brief, sustained MVIC yields a lower value for skeletal muscle oxidative capacity than an MVDC protocol of similar duration and (ii) this difference may not be consistent across populations (e.g., young vs. old). Thus, the potential effect of contraction protocol on comparisons of kPCr in different study groups requires careful consideration in the future.
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Affiliation(s)
- Miles F Bartlett
- Department of KinesiologyMuscle Physiology Laboratory, University of Massachusetts Amherst, MA 01003, USA
| | - Liam F Fitzgerald
- Department of KinesiologyMuscle Physiology Laboratory, University of Massachusetts Amherst, MA 01003, USA
| | - Rajakumar Nagarajan
- Human Magnetic Resonance Center, Institute for Applied Life Sciences (IALS), University of Massachusetts Amherst, MA 01003, USA
| | - Jane A Kent
- Department of KinesiologyMuscle Physiology Laboratory, University of Massachusetts Amherst, MA 01003, USA
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2
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Takeuchi A, Matsuoka S. Integration of mitochondrial energetics in heart with mathematical modelling. J Physiol 2020; 598:1443-1457. [DOI: 10.1113/jp276817] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Accepted: 01/23/2020] [Indexed: 11/08/2022] Open
Affiliation(s)
- Ayako Takeuchi
- Department of Integrative and Systems PhysiologyFaculty of Medical Sciencesand Life Science Innovation CenterUniversity of Fukui Fukui 910‐1193 Japan
| | - Satoshi Matsuoka
- Department of Integrative and Systems PhysiologyFaculty of Medical Sciencesand Life Science Innovation CenterUniversity of Fukui Fukui 910‐1193 Japan
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Goulding RP, Roche DM, Marwood S. Elevated baseline work rate slows pulmonary oxygen uptake kinetics and decreases critical power during upright cycle exercise. Physiol Rep 2018; 6:e13802. [PMID: 30039557 PMCID: PMC6056736 DOI: 10.14814/phy2.13802] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 06/26/2018] [Indexed: 01/08/2023] Open
Abstract
Critical power is a fundamental parameter defining high-intensity exercise tolerance, and is related to the phase II time constant of pulmonary oxygen uptake kinetics (τV˙O2). Whether this relationship is causative is presently unclear. This study determined the impact of raised baseline work rate, which increases τV˙O2, on critical power during upright cycle exercise. Critical power was determined via four constant-power exercise tests to exhaustion in two conditions: (1) with exercise initiated from an unloaded cycling baseline (U→S), and (2) with exercise initiated from a baseline work rate of 90% of the gas exchange threshold (M→S). During these exercise transitions, τV˙O2 and the time constant of muscle deoxyhemoglobin kinetics (τ[HHb + Mb] ) (the latter via near-infrared spectroscopy) were determined. In M→S, critical power was lower (M→S = 203 ± 44 W vs. U→S = 213 ± 45 W, P = 0.011) and τV˙O2 was greater (M→S = 51 ± 14 sec vs. U→S = 34 ± 16 sec, P = 0.002) when compared with U→S. Additionally, τ[HHb + Mb] was greater in M→S compared with U→S (M→S = 28 ± 7 sec vs. U→S = 14 ± 7 sec, P = 0.007). The increase in τV˙O2 and concomitant reduction in critical power in M→S compared with U→S suggests a causal relationship between these two parameters. However, that τ[HHb + Mb] was greater in M→S exculpates reduced oxygen availability as being a confounding factor. These data therefore provide the first experimental evidence that τV˙O2 is an independent determinant of critical power. Keywords critical power, exercise tolerance, oxygen uptake kinetics, power-duration relationship, muscle deoxyhemoglobin kinetics, work-to-work exercise.
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Affiliation(s)
- Richie P. Goulding
- School of Health SciencesLiverpool Hope UniversityLiverpoolUnited Kingdom
| | - Denise M. Roche
- School of Health SciencesLiverpool Hope UniversityLiverpoolUnited Kingdom
| | - Simon Marwood
- School of Health SciencesLiverpool Hope UniversityLiverpoolUnited Kingdom
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Willis WT, Miranda-Grandjean D, Hudgens J, Willis EA, Finlayson J, De Filippis EA, Zapata Bustos R, Langlais PR, Mielke C, Mandarino LJ. Dominant and sensitive control of oxidative flux by the ATP-ADP carrier in human skeletal muscle mitochondria: Effect of lysine acetylation. Arch Biochem Biophys 2018; 647:93-103. [PMID: 29653079 DOI: 10.1016/j.abb.2018.04.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 03/29/2018] [Accepted: 04/08/2018] [Indexed: 02/01/2023]
Abstract
The adenine nucleotide translocase (ANT) of the mitochondrial inner membrane exchanges ADP for ATP. Mitochondria were isolated from human vastus lateralis muscle (n = 9). Carboxyatractyloside titration of O2 consumption rate (Jo) at clamped [ADP] of 21 μM gave ANT abundance of 0.97 ± 0.14 nmol ANT/mg and a flux control coefficient of 82% ± 6%. Flux control fell to 1% ± 1% at saturating (2 mM) [ADP]. The KmADP for Jo was 32.4 ± 1.8 μM. In terms of the free (-3) ADP anion this KmADP was 12.0 ± 0.7 μM. A novel luciferase-based assay for ATP production gave KmADP of 13.1 ± 1.9 μM in the absence of ATP competition. The free anion KmADP in this case was 2.0 ± 0.3 μM. Targeted proteomic analyses showed significant acetylation of ANT Lysine23 and that ANT1 was the most abundant isoform. Acetylation of Lysine23 correlated positively with KmADP, r = 0.74, P = 0.022. The findings underscore the central role played by ANT in the control of oxidative phosphorylation, particularly at the energy phosphate levels associated with low ATP demand. As predicted by molecular dynamic modeling, ANT Lysine23 acetylation decreased the apparent affinity of ADP for ANT binding.
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Affiliation(s)
- W T Willis
- University of Arizona, College of Medicine, Department of Medicine, 1501 N. Campbell Avenue, P.O. Box 245099, Tucson, AZ 85724-5099, USA.
| | - D Miranda-Grandjean
- Mayo Clinic, Division of Endocrinology, East Shea Boulevard and 134th Street, Scottsdale, AZ 85259, USA.
| | - J Hudgens
- Mayo Clinic, Division of Endocrinology, East Shea Boulevard and 134th Street, Scottsdale, AZ 85259, USA.
| | - E A Willis
- Mayo Clinic, Division of Endocrinology, East Shea Boulevard and 134th Street, Scottsdale, AZ 85259, USA.
| | - J Finlayson
- University of Arizona, College of Medicine, Department of Medicine, 1501 N. Campbell Avenue, P.O. Box 245099, Tucson, AZ 85724-5099, USA.
| | - E A De Filippis
- Mayo Clinic, Division of Endocrinology, East Shea Boulevard and 134th Street, Scottsdale, AZ 85259, USA.
| | - R Zapata Bustos
- University of Arizona, College of Medicine, Department of Medicine, 1501 N. Campbell Avenue, P.O. Box 245099, Tucson, AZ 85724-5099, USA.
| | - P R Langlais
- University of Arizona, College of Medicine, Department of Medicine, 1501 N. Campbell Avenue, P.O. Box 245099, Tucson, AZ 85724-5099, USA.
| | - C Mielke
- Mayo Clinic, Division of Endocrinology, East Shea Boulevard and 134th Street, Scottsdale, AZ 85259, USA.
| | - L J Mandarino
- University of Arizona, College of Medicine, Department of Medicine, 1501 N. Campbell Avenue, P.O. Box 245099, Tucson, AZ 85724-5099, USA.
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Tissue Type-Specific Bioenergetic Abnormalities in Adults with Major Depression. Neuropsychopharmacology 2017; 42:876-885. [PMID: 27585738 PMCID: PMC5312061 DOI: 10.1038/npp.2016.180] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Revised: 08/11/2016] [Accepted: 08/27/2016] [Indexed: 11/08/2022]
Abstract
Brain bioenergetic abnormalities have been observed frequently in adults with major depressive disorder (MDD); however, results have been inconsistent regarding whether decreased or increased metabolism was observed. Phosphorus-31 magnetic resonance spectroscopy (31P MRS) allows for the quantification of bioenergetic molecules, containing high-energy phosphates, over the whole brain as well as measuring the differences between gray matter and white matter. We recruited 50 subjects with a current diagnosis of MDD, not currently treated with psychotropic medication, between ages of 18 and 65 (mean±SD age: 43.4±13.6; 46% female) and 30 healthy volunteers, matched for age and gender (39.0±12.5 years of age; 36.6% female). All subjects received a T1 MP-FLASH scan for tissue segmentation followed by 31P MRS, chemical shift imaging scan with 84 voxels of data collected over the entire brain utilizing a dual-tuned, proton-phosphorus coil to minimize subject movement. Phosphocreatine and inorganic phosphate (Pi) varied in opposite directions across gray matter and white matter when MDD subjects were compared with controls. This finding suggests alterations in high-energy phosphate metabolism and regulation of oxidative phosphorylation in MDD patients. In addition, within the MDD group, gray matter Pi, a regulator of oxidative phosphorylation, correlated positively with severity of depression. These data support a model that includes changes in brain bioenergetic function in subjects with major depression.
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Harper DG, Joe EB, Jensen JE, Ravichandran C, Forester BP. Brain levels of high-energy phosphate metabolites and executive function in geriatric depression. Int J Geriatr Psychiatry 2016; 31:1241-1249. [PMID: 26891040 DOI: 10.1002/gps.4439] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 12/29/2015] [Accepted: 01/05/2016] [Indexed: 11/05/2022]
Abstract
OBJECTIVES Depression in late life has been associated with difficulties in cognitive processing, particularly in the domains of executive function, processing speed and memory, and increases the risk of developing dementia suggesting a neurodegenerative phenotype. Mitochondrial dysfunction is frequently an early event in neurodegenerative illnesses and may be operative in patients with late life depression. Phosphorus magnetic resonance spectroscopy (31P MRS) allows for the quantification of bioenergetic molecules produced by mitochondria. METHODS Ten patients with late life depression and eight normal elderly controls were studied with Stroop color and interference tests, which are widely used measures of processing speed and executive function, respectively, followed by (31P) MRS 3-dimensional chemical-shift imaging measuring levels of adenosine triphosphate, phosphocreatine, inorganic phosphate, and pH over the whole brain. RESULTS In all subjects, gray matter phosphocreatine was positively associated with Stroop interference. Levels of white matter adenosine triphosphate were associated with Stroop interference in subjects with late life depression but not normal elderly. There was also a complementary association between white matter inorganic phosphate and Stroop interference in late life depression patients. CONCLUSIONS These findings suggest two independent sources of executive function dependence on bioenergetic state in the aging brain. The dependence of executive function performance in subjects with late life depression on ATP in white matter may be associated with mitochondrial impairment and is consistent with predictions of the vascular depression hypothesis. Further research with wider neuropsychological testing targeting bioenergetic markers could help clarify the scope of these effects. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- David G Harper
- Geriatric Psychiatry Program, McLean Hospital, Belmont, MA, USA. .,Harvard Medical School, Boston, MA, USA.
| | | | - J Eric Jensen
- Neuroimaging Center, McLean Hospital, Belmont, MA, USA.,Harvard Medical School, Boston, MA, USA
| | - Caitlin Ravichandran
- Laboratory for Psychiatric Biostatistics, McLean Hospital, Belmont, MA, USA.,Harvard Medical School, Boston, MA, USA
| | - Brent P Forester
- Geriatric Psychiatry Program, McLean Hospital, Belmont, MA, USA.,Harvard Medical School, Boston, MA, USA
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Li M, Chen F, Wang H, Wu W, Zhang X, Tian C, Yu H, Liu R, Zhu B, Zhang B, Dai Z. Non-invasive assessment of phosphate metabolism and oxidative capacity in working skeletal muscle in healthy young Chinese volunteers using (31)P Magnetic Resonance Spectroscopy. PeerJ 2016; 4:e2259. [PMID: 27547565 PMCID: PMC4963215 DOI: 10.7717/peerj.2259] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 06/24/2016] [Indexed: 11/25/2022] Open
Abstract
Background. Generally, males display greater strength and muscle capacity than females while performing a task. Muscle biopsy is regarded as the reference method of evaluating muscle functions; however, it is invasive and has sampling errors, and is not practical for longitudinal studies and dynamic measurement during excise. In this study, we built an in-house force control and gauge system for quantitatively applying force to quadriceps while the subjects underwent 31P Magnetic Resonance Spectroscopy (31P-MRS); our aim was to investigate if there is a sex difference of phosphate metabolite change in working muscles in young heathy Chinese volunteers. Methods. Volunteers performed knee-extending excises using a force control and gauge system while lying prone in a Philips 3T Magnetic Resonance (MR) scanner. The 31P-MRS coil was firmly placed under the middle of the quadriceps . 31P-MRS measurements of inorganic phosphate (Pi), phosphocreatine (PCr) and adenosine triphosphate (ATP) were acquired from quadriceps while subjects were in a state of pre-, during- and post-exercise. The PCr, Pi, PCr/Pi, PCr/ATP, pH, work/energy cost ratio (WE), kPCr and oxidative capacity were compared between males and females. Results. A total of 17 volunteers underwent the study. Males: N = 10, age = 23.30 ± 1.25years; females: N = 7, age = 23.57 ± 0.79 years. In this study, males had significantly greater WE (16.33 ± 6.46 vs. 7.82 ± 2.16, p = 0.002) than females. Among PCr, Pi, PCr/Pi, PCr/ATP, pH, kPCr and oxidative capacity at different exercise status, only PCr/Pi (during-exercise, males = 5.630 ± 1.647, females = 4.014 ± 1.298, p = 0.047), PCr/ATP (during-exercise, males =1.273 ± 0.219, females = 1.523 ± 0.167, p = 0.025), and ATP (post-exercise, males = 24.469 ± 3.911 mmol/kg, females = 18.353 ± 4.818 mmol/kg, p = 0.035) had significant sex differences. Males had significantly greater PCr/Pi, but less PCr/ATP than females during exercise, suggesting males had higher energy transfer efficiency than females. At the post-exercise status, the recovery of PCr did not show sex difference. Conclusions. Our in-house force control and gauge system quantitatively applied force during the exercise for 31P-MRS experiments, and a sex difference of higher energy transfer efficiency and WE was detected in males with mild loaded exercising quadriceps. This noninvasive technology allows us to further study and understand the sex difference of high energy phosphate metabolism in the future.
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Affiliation(s)
- Ming Li
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, Jiangsu, China
| | - Fei Chen
- Department of Radiology, Affiliated Yancheng Hospital, School of Medicine, Southeast University, Yancheng, Jiangsu, China
| | - Huiting Wang
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, Jiangsu, China
| | - Wenbo Wu
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, Jiangsu, China
| | - Xin Zhang
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, Jiangsu, China
| | - Chuanshuai Tian
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, Jiangsu, China
| | - Haiping Yu
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, Jiangsu, China
| | - Renyuan Liu
- Department of Neurology, Drum Tower Hospital, Affiliated to Nanjing University Medical School, Nanjing, Jiangsu, China
| | - Bin Zhu
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, Jiangsu, China
| | - Bing Zhang
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, Jiangsu, China
| | - Zhenyu Dai
- Department of Radiology, Affiliated Yancheng Hospital, School of Medicine, Southeast University, Yancheng, Jiangsu, China
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Yano T, Afroundeh R, Shirakawa K, Lian CS, Shibata K, Xiao Z, Yunoki T. Oscillation in tissue oxygen index during recovery from exercise. Physiol Res 2016; 65:259-69. [PMID: 26447517 DOI: 10.33549/physiolres.933044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
It was hypothesized that an oscillation of tissue oxygen index (TOI) determined by near-infrared spectroscopy during recovery from exercise occurs due to feedback control of adenosine triphosphate and that frequency of the oscillation is affected by blood pH. In order to examine these hypotheses, we aimed 1) to determine whether there is an oscillation of TOI during recovery from exercise and 2) to determine the effect of blood pH on frequency of the oscillation of TOI. Three exercises were performed with exercise intensities of 30 % and 70 % peak oxygen uptake (V(.)o(2)peak) for 12 min and with exercise intensity of 70 % V(.)o(2)peak for 30 s. TOI during recovery from the exercise was analyzed by fast Fourier transform in order to obtain power spectra density (PSD). There was a significant difference in the frequency at which maximal PSD of TOI appeared (Fmax) between the exercises with 70 % V(.)o(2)peak for 12 min (0.0039+/-0 Hz) and for 30 s (0.0061+/-0.0028 Hz). However, there was no significant difference in Fmax between the exercises with 30 % (0.0043+/-0.0013 Hz) and with 70 % V(.)o(2)peak for 12 min despite differences in blood pH and blood lactate from the warmed fingertips. It is concluded that there was an oscillation in TOI during recovery from the three exercises. It was not clearly shown that there was an effect of blood pH on Fmax.
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Affiliation(s)
- T Yano
- Department of Human Developmental Sciences, Faculty of Education, Hokkaido University, Kita-ku, Japan.
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Kemp GJ, Ahmad RE, Nicolay K, Prompers JJ. Quantification of skeletal muscle mitochondrial function by 31P magnetic resonance spectroscopy techniques: a quantitative review. Acta Physiol (Oxf) 2015; 213:107-44. [PMID: 24773619 DOI: 10.1111/apha.12307] [Citation(s) in RCA: 102] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2013] [Revised: 12/30/2013] [Accepted: 04/23/2014] [Indexed: 12/16/2022]
Abstract
Magnetic resonance spectroscopy (MRS) can give information about cellular metabolism in vivo which is difficult to obtain in other ways. In skeletal muscle, non-invasive (31) P MRS measurements of the post-exercise recovery kinetics of pH, [PCr], [Pi] and [ADP] contain valuable information about muscle mitochondrial function and cellular pH homeostasis in vivo, but quantitative interpretation depends on understanding the underlying physiology. Here, by giving examples of the analysis of (31) P MRS recovery data, by some simple computational simulation, and by extensively comparing data from published studies using both (31) P MRS and invasive direct measurements of muscle O2 consumption in a common analytical framework, we consider what can be learnt quantitatively about mitochondrial metabolism in skeletal muscle using MRS-based methodology. We explore some technical and conceptual limitations of current methods, and point out some aspects of the physiology which are still incompletely understood.
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Affiliation(s)
- G. J. Kemp
- Department of Musculoskeletal Biology, and Magnetic Resonance and Image Analysis Research Centre; University of Liverpool; Liverpool UK
| | - R. E. Ahmad
- Department of Musculoskeletal Biology, and Magnetic Resonance and Image Analysis Research Centre; University of Liverpool; Liverpool UK
| | - K. Nicolay
- Biomedical NMR; Department of Biomedical Engineering; Eindhoven University of Technology; Eindhoven the Netherlands
| | - J. J. Prompers
- Biomedical NMR; Department of Biomedical Engineering; Eindhoven University of Technology; Eindhoven the Netherlands
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Plante DT, Trksak GH, Jensen JE, Penetar DM, Ravichandran C, Riedner BA, Tartarini WL, Dorsey CM, Renshaw PF, Lukas SE, Harper DG. Gray matter-specific changes in brain bioenergetics after acute sleep deprivation: a 31P magnetic resonance spectroscopy study at 4 Tesla. Sleep 2014; 37:1919-27. [PMID: 25325507 DOI: 10.5665/sleep.4242] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Accepted: 07/03/2014] [Indexed: 01/21/2023] Open
Abstract
STUDY OBJECTIVES A principal function of sleep may be restoration of brain energy metabolism caused by the energetic demands of wakefulness. Because energetic demands in the brain are greater in gray than white matter, this study used linear mixed-effects models to examine tissue-type specific changes in high-energy phosphates derived using 31P magnetic resonance spectroscopy (MRS) after sleep deprivation and recovery sleep. DESIGN Experimental laboratory study. SETTING Outpatient neuroimaging center at a private psychiatric hospital. PARTICIPANTS A total of 32 MRS scans performed in eight healthy individuals (mean age 35 y; range 23-51 y). INTERVENTIONS Phosphocreatine (PCr) and β-nucleoside triphosphate (NTP) were measured using 31P MRS three dimensional-chemical shift imaging at high field (4 Tesla) after a baseline night of sleep, acute sleep deprivation (SD), and 2 nights of recovery sleep. Novel linear mixed-effects models were constructed using spectral and tissue segmentation data to examine changes in bioenergetics in gray and white matter. MEASUREMENTS AND RESULTS PCr increased in gray matter after 2 nights of recovery sleep relative to SD with no significant changes in white matter. Exploratory analyses also demonstrated that increases in PCr were associated with increases in electroencephalographic slow wave activity during recovery sleep. No significant changes in β-NTP were observed. CONCLUSIONS These results demonstrate that sleep deprivation and subsequent recovery-induced changes in high-energy phosphates primarily occur in gray matter, and increases in PCr after recovery sleep may be related to sleep homeostasis.
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Affiliation(s)
- David T Plante
- Department of Psychiatry, University of Wisconsin School of Medicine and Public Health, Madison, WI
| | - George H Trksak
- Behavioral Psychopharmacology Research Lab, McLean Hospital, Belmont, MA: Brain Imaging Center, McLean Hospital, Belmont, MA: Sleep Research Laboratory, McLean Hospital, Belmont, MA: Harvard Medical School, Boston, MA
| | - J Eric Jensen
- Brain Imaging Center, McLean Hospital, Belmont, MA: Harvard Medical School, Boston, MA
| | - David M Penetar
- Behavioral Psychopharmacology Research Lab, McLean Hospital, Belmont, MA: Brain Imaging Center, McLean Hospital, Belmont, MA: Sleep Research Laboratory, McLean Hospital, Belmont, MA: Harvard Medical School, Boston, MA
| | - Caitlin Ravichandran
- Harvard Medical School, Boston, MA: Laboratory for Psychiatric Biostatistics, McLean Hospital, Belmont, MA
| | - Brady A Riedner
- Department of Psychiatry, University of Wisconsin School of Medicine and Public Health, Madison, WI
| | | | - Cynthia M Dorsey
- Brain Imaging Center, McLean Hospital, Belmont, MA: Sleep Research Laboratory, McLean Hospital, Belmont, MA: Harvard Medical School, Boston, MA
| | - Perry F Renshaw
- The Brain Institute, University of Utah School of Medicine, Salt Lake City, UT
| | - Scott E Lukas
- Behavioral Psychopharmacology Research Lab, McLean Hospital, Belmont, MA: Brain Imaging Center, McLean Hospital, Belmont, MA: Sleep Research Laboratory, McLean Hospital, Belmont, MA: Harvard Medical School, Boston, MA
| | - David G Harper
- Harvard Medical School, Boston, MA: Geriatric Psychiatry Program, McLean Hospital, Belmont, MA
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11
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Larsen RG, Maynard L, Kent JA. High-intensity interval training alters ATP pathway flux during maximal muscle contractions in humans. Acta Physiol (Oxf) 2014; 211:147-60. [PMID: 24612773 DOI: 10.1111/apha.12275] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2013] [Revised: 02/18/2014] [Accepted: 03/05/2014] [Indexed: 12/15/2022]
Abstract
AIM High-intensity interval training (HIT) results in potent metabolic adaptations in skeletal muscle; however, little is known about the influence of these adaptations on energetics in vivo. We used magnetic resonance spectroscopy to examine the effects of HIT on ATP synthesis from net PCr breakdown (ATPCK ), oxidative phosphorylation (ATPOX ) and non-oxidative glycolysis (ATPGLY ) in vivo in vastus lateralis during a 24-s maximal voluntary contraction (MVC). METHODS Eight young men performed 6 sessions of repeated, 30-s 'all-out' sprints on a cycle ergometer; measures of muscle energetics were obtained at baseline and after the first and sixth sessions. RESULTS Training increased peak oxygen consumption (35.8 ± 1.4 to 39.3 ± 1.6 mL min(-1) kg(-1) , P = 0.01) and exercise capacity (217.0 ± 11.0 to 230.5 ± 11.7 W, P = 0.04) on the ergometer, with no effects on total ATP production or force-time integral during the MVC. While ATP production by each pathway was unchanged after the first session, 6 sessions increased the relative contribution of ATPOX (from 31 ± 2 to 39 ± 2% of total ATP turnover, P < 0.001) and lowered the relative contribution from both ATPCK (49 ± 2 to 44 ± 1%, P = 0.004) and ATPGLY (20 ± 2 to 17 ± 1%, P = 0.03). CONCLUSION These alterations to muscle ATP production in vivo indicate that brief, maximal contractions are performed with increased support of oxidative ATP synthesis and relatively less contribution from anaerobic ATP production following training. These results extend previous reports of molecular and cellular adaptations to HIT and show that 6 training sessions are sufficient to alter in vivo muscle energetics, which likely contributes to increased exercise capacity after short-term HIT.
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Affiliation(s)
- R. G. Larsen
- Department of Kinesiology; University of Massachusetts; Amherst MA USA
- Department of Health Science and Technology; Aalborg University; Aalborg Denmark
| | - L. Maynard
- Department of Kinesiology; University of Massachusetts; Amherst MA USA
| | - J. A. Kent
- Department of Kinesiology; University of Massachusetts; Amherst MA USA
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12
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Buyandelger B, Mansfield C, Knöll R. Mechano-signaling in heart failure. Pflugers Arch 2014; 466:1093-9. [PMID: 24531746 PMCID: PMC4033803 DOI: 10.1007/s00424-014-1468-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Revised: 01/29/2014] [Accepted: 01/30/2014] [Indexed: 02/07/2023]
Abstract
Mechanosensation and mechanotransduction are fundamental aspects of biology, but the link between physical stimuli and biological responses remains not well understood. The perception of mechanical stimuli, their conversion into biochemical signals, and the transmission of these signals are particularly important for dynamic organs such as the heart. Various concepts have been introduced to explain mechanosensation at the molecular level, including effects on signalosomes, tensegrity, or direct activation (or inactivation) of enzymes. Striated muscles, including cardiac myocytes, differ from other cells in that they contain sarcomeres which are essential for the generation of forces and which play additional roles in mechanosensation. The majority of cardiomyopathy causing candidate genes encode structural proteins among which titin probably is the most important one. Due to its elastic elements, titin is a length sensor and also plays a role as a tension sensor (i.e., stress sensation). The recent discovery of titin mutations being a major cause of dilated cardiomyopathy (DCM) also underpins the importance of mechanosensation and mechanotransduction in the pathogenesis of heart failure. Here, we focus on sarcomere-related mechanisms, discuss recent findings, and provide a link to cardiomyopathy and associated heart failure.
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Affiliation(s)
- Byambajav Buyandelger
- Imperial College, British Heart Foundation-Centre for Research Excellence, National Heart and Lung Institute, Imperial Centre for Translational and Experimental Medicine, Hammersmith Campus, Du Cane Road, London, W12 0NN, UK
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13
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Wüst RCI, McDonald JR, Sun Y, Ferguson BS, Rogatzki MJ, Spires J, Kowalchuk JM, Gladden LB, Rossiter HB. Slowed muscle oxygen uptake kinetics with raised metabolism are not dependent on blood flow or recruitment dynamics. J Physiol 2014; 592:1857-71. [PMID: 24469073 DOI: 10.1113/jphysiol.2013.267476] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Oxygen uptake kinetics (τVO2) are slowed when exercise is initiated from a raised metabolic rate. Whether this reflects the recruitment of muscle fibres differing in oxidative capacity, or slowed blood flow (Q) kinetics is unclear. This study determined τVO2 in canine muscle in situ, with experimental control over muscle activation and Q during contractions initiated from rest and a raised metabolic rate. The gastrocnemius complex of nine anaesthetised, ventilated dogs was isolated and attached to a force transducer. Isometric tetanic contractions (50 Hz; 200 ms duration) via supramaximal sciatic nerve stimulation were used to manipulate metabolic rate: 3 min stimulation at 0.33 Hz (S1), followed by 3 min at 0.67 Hz (S2). Circulation was initially intact (SPON), and subsequently isolated for pump-perfusion (PUMP) above the greatest value in SPON. Muscle VO2 was determined contraction-by-contraction using an ultrasonic flowmeter and venous oximeter, and normalised to tension-time integral (TTI). τVO2/TTI and τQ were less in S1SPON (mean ± s.d.: 13 ± 3 s and 12 ± 4 s, respectively) than in S2SPON (29 ± 19 s and 31 ± 13 s, respectively; P < 0.05). τVO2/TTI was unchanged by pump-perfusion (S1PUMP, 12 ± 4 s; S2PUMP, 24 ± 6 s; P < 0.001) despite increased O2 delivery; at S2 onset, venous O2 saturation was 21 ± 4% and 65 ± 5% in SPON and PUMP, respectively. VO2 kinetics remained slowed when contractions were initiated from a raised metabolic rate despite uniform muscle stimulation and increased O2 delivery. The intracellular mechanism may relate to a falling energy state, approaching saturating ADP concentration, and/or slowed mitochondrial activation; but further study is required. These data add to the evidence that muscle VO2 control is more complex than previously suggested.
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Affiliation(s)
- Rob C I Wüst
- Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W. Carson Street, CDCRC Building, Torrance, CA 90502, USA.
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14
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Korzeniewski B. Regulation of oxidative phosphorylation during work transitions results from its kinetic properties. J Appl Physiol (1985) 2013; 116:83-94. [PMID: 24157529 DOI: 10.1152/japplphysiol.00759.2013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The regulation of oxidative phosphorylation (OXPHOS) during work transitions in skeletal muscle and heart is still not well understood. Different computer models of this process have been developed that are characterized by various kinetic properties. In the present research-polemic theoretical study it is argued that models belonging to one group (Model A), which predict that among OXPHOS complexes complex III keeps almost all of the metabolic control over oxygen consumption (Vo2) and involve a strong complex III activation by inorganic phosphate (Pi), lead to the conclusion that an increase in Pi is the main mechanism responsible for OXPHOS activation (feedback-activation mechanism). Models belonging to another group (Model B), which were developed to take into account an approximately uniform distribution of metabolic control over Vo2 among particular OXPHOS complexes (complex I, complex III, complex IV, ATP synthase, ATP/ADP carrier, phosphate carrier) encountered in experimental studies in isolated mitochondria, predict that all OXPHOS complexes are directly activated in parallel with ATP usage and NADH supply by some external cytosolic factor/mechanism during rest-to-work or low-to-high work transitions in skeletal muscle and heart ("each-step-activation" mechanism). Model B demonstrates that different intensities of each-step activation can account for the very different (slopes of) phenomenological Vo2-ADP relationships observed in various skeletal muscles and heart. Thus they are able to explain the differences in the regulation of OXPHOS during work transitions between skeletal muscle (where moderate changes in ADP take place) and intact heart in vivo (where ADP is essentially constant).
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Affiliation(s)
- Bernard Korzeniewski
- Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland
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15
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van Oorschot JWM, Schmitz JPJ, Webb A, Nicolay K, Jeneson JAL, Kan HE. 31P MR spectroscopy and computational modeling identify a direct relation between Pi content of an alkaline compartment in resting muscle and phosphocreatine resynthesis kinetics in active muscle in humans. PLoS One 2013; 8:e76628. [PMID: 24098796 PMCID: PMC3786961 DOI: 10.1371/journal.pone.0076628] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Accepted: 08/26/2013] [Indexed: 12/04/2022] Open
Abstract
The assessment of mitochondrial properties in skeletal muscle is important in clinical research, for instance in the study of diabetes. The gold standard to measure mitochondrial capacity non-invasively is the phosphocreatine (PCr) recovery rate after exercise, measured by (31)P Magnetic Resonance spectroscopy ((31)P MRS). Here, we sought to expand the evidence base for an alternative method to assess mitochondrial properties which uses (31)P MRS measurement of the Pi content of an alkaline compartment attributed to mitochondria (Pi2; as opposed to cytosolic Pi (Pi1)) in resting muscle at high magnetic field. Specifically, the PCr recovery rate in human quadriceps muscle was compared with the signal intensity of the Pi2 peak in subjects with varying mitochondrial content of the quadriceps muscle as a result of athletic training, and the results were entered into a mechanistic computational model of mitochondrial metabolism in muscle to test if the empirical relation between Pi2/Pi1 ratio and the PCr recovery was consistent with theory. Localized (31)P spectra were obtained at 7T from resting vastus lateralis muscle to measure the intensity of the Pi2 peak. In the endurance trained athletes a Pi2/Pi1 ratio of 0.07 ± 0.01 was found, compared to a significantly lower (p<0.05) Pi2/Pi1 ratio of 0.03 ± 0.01 in the normally active group. Next, PCr recovery kinetics after in magnet bicycle exercise were measured at 1.5T. For the endurance trained athletes, a time constant τPCr 12 ± 3 s was found, compared to 24 ± 5s in normally active subjects. Without any parameter optimization the computational model prediction matched the experimental data well (r(2) of 0.75). Taken together, these results suggest that the Pi2 resonance in resting human skeletal muscle observed at 7T provides a quantitative MR-based functional measure of mitochondrial density.
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Affiliation(s)
| | - Joep P. J. Schmitz
- Systems Bioinformatics, Amsterdam Institute for Molecules, Medicines and Systems (AIMMS), VU University Amsterdam, Amsterdam, The Netherlands
- Computational Biology group, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Andrew Webb
- CJ Gorter Center for High field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Klaas Nicolay
- Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Jeroen A. L. Jeneson
- Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
- Laboratory for Liver, Digestive and Metabolic Disease, University Medical Center Groningen, Groningen, The Netherlands
| | - Hermien E. Kan
- CJ Gorter Center for High field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
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van Riel NAW, Tiemann CA, Vanlier J, Hilbers PAJ. Applications of analysis of dynamic adaptations in parameter trajectories. Interface Focus 2013; 3:20120084. [PMID: 23853705 PMCID: PMC3638482 DOI: 10.1098/rsfs.2012.0084] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Metabolic profiling in combination with pathway-based analyses and computational modelling are becoming increasingly important in clinical and preclinical research. Modelling multi-factorial, progressive diseases requires the integration of molecular data at the metabolome, proteome and transcriptome levels. Also the dynamic interaction of organs and tissues needs to be considered. The processes involved cover time scales that are several orders of magnitude different. We report applications of a computational approach to bridge the scales and different levels of biological detail. Analysis of dynamic adaptations in parameter trajectories (ADAPTs) aims to investigate phenotype transitions during disease development and after a therapeutic intervention. ADAPT is based on a time-dependent evolution of model parameters to describe the dynamics of metabolic adaptations. The progression of metabolic adaptations is predicted by identifying necessary dynamic changes in the model parameters to describe the transition between experimental data obtained during different stages. To get a better understanding of the concept, the ADAPT approach is illustrated in a theoretical study. Its application in research on progressive changes in lipoprotein metabolism is also discussed.
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Affiliation(s)
- Natal A W van Riel
- Department of Biomedical Engineering , Eindhoven University of Technology , Den Dolech 2, Eindhoven, 5612 AZ , The Netherlands ; Institute for Complex Molecular Systems , Eindhoven University of Technology , Den Dolech 2, Eindhoven, 5612 AZ , The Netherlands ; Netherlands Consortium for Systems Biology , University of Amsterdam , Science Park 904, Amsterdam, 1098 XH , The Netherlands
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Larsen RG, Befroy DE, Kent-Braun JA. High-intensity interval training increases in vivo oxidative capacity with no effect on P(i)→ATP rate in resting human muscle. Am J Physiol Regul Integr Comp Physiol 2012; 304:R333-42. [PMID: 23255590 DOI: 10.1152/ajpregu.00409.2012] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Mitochondrial ATP production is vital for meeting cellular energy demand at rest and during periods of high ATP turnover. We hypothesized that high-intensity interval training (HIT) would increase ATP flux in resting muscle (VPi→ATP) in response to a single bout of exercise, whereas changes in the capacity for oxidative ATP production (Vmax) would require repeated bouts. Eight untrained men (27 ± 4 yr; peak oxygen uptake = 36 ± 4 ml·kg(-1)·min(-1)) performed six sessions of HIT (4-6 × 30-s bouts of all-out cycling with 4-min recovery). After standardized meals and a 10-h fast, VPi→ATP and Vmax of the vastus lateralis muscle were measured using phosphorus magnetic resonance spectroscopy at 4 Tesla. Measurements were obtained at baseline, 15 h after the first training session, and 15 h after completion of the sixth session. VPi→ATP was determined from the unidirectional flux between Pi and ATP, using the saturation transfer technique. The rate of phosphocreatine recovery (kPCr) following a maximal contraction was used to calculate Vmax. While kPCr and Vmax were unchanged after a single session of HIT, completion of six training sessions resulted in a ∼14% increase in muscle oxidative capacity (P ≤ 0.004). In contrast, neither a single nor six training sessions altered VPi→ATP (P = 0.74). This novel analysis of resting and maximal high-energy phosphate kinetics in vivo in response to HIT provides evidence that distinct aspects of human skeletal muscle metabolism respond differently to this type of training.
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Affiliation(s)
- Ryan G Larsen
- Department of Kinesiology, University of Massachusetts, Amherst, MA 01003, USA
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18
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Wüst RCI, van der Laarse WJ, Rossiter HB. On-off asymmetries in oxygen consumption kinetics of single Xenopus laevis skeletal muscle fibres suggest higher-order control. J Physiol 2012; 591:731-44. [PMID: 23165768 DOI: 10.1113/jphysiol.2012.241992] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The mechanisms controlling skeletal muscle oxygen consumption (V(o)₂) during exercise are not well understood. We determined whether first-order control could explain V(o)₂kinetics at contractions onset (V(o)₂(on)) and cessation (V(o)₂off)) in single skeletal muscle fibres differing in oxdidative capacity, and across stimulation intensities up to V(o)₂(max). Xenopus laevis fibres (n = 21) were suspended in a sealed chamber with a fast response P(o)₂ electrode to measure V(o)₂ every second before, during and after stimulated isometric contractions. A first-order model did not well characterize on-transient V(o)₂ kinetics. Including a time delay (TD) in the model provided a significantly improved characterization than a first-order fit without TD (F-ratio; P < 0.05), and revealed separate 'activation' and 'exponential' phases in 15/21 fibres contracting at V(o)₂(max) (mean ± SD TD: 14 ± 3s). On-transient kinetics (τV(o)₂(on)) was weakly and linearly related to V(o)₂(max) (R² = 0.271, P = 0.015). Off-transient kinetics, however, were first-order, and τV(o)₂(off) was greater in low-oxidative (V(o)₂max < 0.05 nmol mm⁻³s⁻¹ than high-oxidative fibres (V(o)₂(max > 0.10 nmol mm ⁻³ s⁻¹; 170 ± 70 vs. 29 ± 6 s, P < 0.001). 1/ τV(o)₂(off) was proportional to V(o)₂(max) (R² = 0.727, P < 0.001), unlike in the on-transient. The calculated oxygen deficit was larger (P < 0.05) than the post-contraction volume of consumed oxygen at all intensities except V(o)₂(max). These data show a clear dissociation between the kinetic control of V(o)₂at the onset and cessation of contractions and across stimulation intensities. More complex models are therefore required to understand the activation of mitochondrial respiration in skeletal muscle at the start of exercise.
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Affiliation(s)
- Rob C I Wüst
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, UK
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19
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Abstract
Current concepts of mechanosensation are general and applicable to almost every cell type. However, striated muscle cells are distinguished by their ability to generate strong forces via actin/myosin interaction, and this process is fine-tuned for optimum contractility. This aspect, unique for actively contracting cells, may be defined as "sensing of the magnitude and dynamics of contractility," as opposed to the well-known concepts of the "perception of extracellular mechanical stimuli." The acto/myosin interaction, by producing changes in ATP, ADP, Pi, and force on a millisecond timescale, may be regarded as a novel and previously unappreciated mechanosensory mechanism. In addition, sarcomeric mechanosensory structures, such as the Z-disc, are directly linked to autophagy, survival, and cell death-related pathways. One emerging example is telethonin and its ability to interfere with p53 metabolism and hence apoptosis (mechanoptosis). In this article, we introduce contractility per se as an important mechanosensory mechanism, and we differentiate extracellular from intracellular mechanosensory effects.
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Affiliation(s)
- Ralph Knöll
- Heart Science Section, National Heart & Lung Institute, Imperial College, London W12 0NN, UK.
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Mansfield C, West TG, Curtin NA, Ferenczi MA. Stretch of contracting cardiac muscle abruptly decreases the rate of phosphate release at high and low calcium. J Biol Chem 2012; 287:25696-705. [PMID: 22692210 PMCID: PMC3406658 DOI: 10.1074/jbc.m112.373498] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Revised: 05/25/2012] [Indexed: 11/06/2022] Open
Abstract
The contractile performance of the heart is linked to the energy that is available to it. Yet, the heart needs to respond quickly to changing demands. During diastole, the heart fills with blood and the heart chambers expand. Upon activation, contraction of cardiac muscle expels blood into the circulation. Early in systole, parts of the left ventricle are being stretched by incoming blood, before contraction causes shrinking of the ventricle. We explore here the effect of stretch of contracting permeabilized cardiac trabeculae of the rat on the rate of inorganic phosphate (P(i)) release resulting from ATP hydrolysis, using a fluorescent sensor for P(i) with millisecond time resolution. Stretch immediately reduces the rate of P(i) release, an effect observed both at full calcium activation (32 μmol/liter of Ca(2+)), and at a physiological activation level of 1 μmol/liter of Ca(2+). The results suggest that stretch redistributes the actomyosin cross-bridges toward their P(i)-containing state. The redistribution means that a greater fraction of cross-bridges will be poised to rapidly produce a force-generating transition and movement, compared with cross-bridges that have not been subjected to stretch. At the same time stretch modifies the P(i) balance in the cytoplasm, which may act as a cytoplasmic signal for energy turnover.
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Affiliation(s)
- Catherine Mansfield
- From the Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London SW7 2AZ and
| | - Tim G. West
- the Royal Veterinary College, University of London, Hertfordshire AL9 7TA,United Kingdom
| | - Nancy A. Curtin
- From the Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London SW7 2AZ and
| | - Michael A. Ferenczi
- From the Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London SW7 2AZ and
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