1
|
Bajpeyi S, Pasarica M, Conley KE, Newcomer BR, Jubrias SA, Gamboa C, Murray K, Sereda O, Sparks LM, Smith SR. Pioglitazone-induced improvements in insulin sensitivity occur without concomitant changes in muscle mitochondrial function. Metabolism 2017; 69:24-32. [PMID: 28285649 DOI: 10.1016/j.metabol.2016.11.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 11/19/2016] [Accepted: 11/29/2016] [Indexed: 12/16/2022]
Abstract
AIMS Pioglitazone (Pio) is known to improve insulin sensitivity in skeletal muscle. However, the role of Pio in skeletal muscle lipid metabolism and skeletal muscle oxidative capacity is not clear. The aim of this study was to determine the effects of chronic Pio treatment on skeletal muscle mitochondrial activity in individuals with type 2 diabetes (T2D). MATERIALS AND METHODS Twenty-four participants with T2D (13M/11F 53.38±2.1years; BMI 36.47±1.1kg/m2) were randomized to either a placebo (CON, n=8) or a pioglitazone (PIO, n=16) group. Following 12weeks of treatment, we measured insulin sensitivity by hyperinsulinemic-euglycemic clamp (clamp), metabolic flexibility by calculating the change in respiratory quotient (ΔRQ) during the steady state of the clamp, intra- and extra-myocellular lipid content (IMCL and EMCL, respectively) by 1H magnetic resonance spectroscopy (1H-MRS) and muscle maximal ATP synthetic capacity (ATPmax) by 31P-MRS. RESULTS Following 12weeks of PIO treatment, insulin sensitivity (p<0.0005 vs. baseline) and metabolic flexibility (p<0.05 vs. CON) significantly increased. PIO treatment significantly decreased IMCL content and increased EMCL content in gastrocnemius, soleus and tibialis anterior muscles. ATPmax was unaffected by PIO treatment. CONCLUSIONS These results suggest that 12weeks of pioglitazone treatment improves insulin sensitivity, metabolic flexibility and myocellular lipid distribution without any effect on maximal ATP synthetic capacity in skeletal muscle. Consequently, pioglitazone-induced enhancements in insulin responsiveness and fuel utilization are independent of mitochondrial function.
Collapse
Affiliation(s)
- Sudip Bajpeyi
- Pennington Biomedical Research Center, 6400 Perkins Road, Baton Rouge, LA 70808, USA; Department of Kinesiology, University of Texas in El Paso, 500 University Ave, El Paso, TX 79968, USA
| | - Magdalena Pasarica
- Translational Research Institute for Metabolism and Diabetes, Florida Hospital, Orlando, FL 32804, USA
| | - Kevin E Conley
- Department of Radiology, University of Washington Medical Center, 1959 NE Pacific St, Seattle, WA 98195, USA
| | - Bradley R Newcomer
- Department of Clinical and Diagnostic Sciences, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Sharon A Jubrias
- Department of Radiology, University of Washington Medical Center, 1959 NE Pacific St, Seattle, WA 98195, USA
| | - Cecilia Gamboa
- Department of Kinesiology, University of Texas in El Paso, 500 University Ave, El Paso, TX 79968, USA
| | - Kori Murray
- Pennington Biomedical Research Center, 6400 Perkins Road, Baton Rouge, LA 70808, USA
| | - Olga Sereda
- Pennington Biomedical Research Center, 6400 Perkins Road, Baton Rouge, LA 70808, USA
| | - Lauren M Sparks
- Translational Research Institute for Metabolism and Diabetes, Florida Hospital, Orlando, FL 32804, USA; Sanford Burnham Prebys Medical Discovery Institute, Orlando, FL 32827, USA
| | - Steven R Smith
- Translational Research Institute for Metabolism and Diabetes, Florida Hospital, Orlando, FL 32804, USA; Sanford Burnham Prebys Medical Discovery Institute, Orlando, FL 32827, USA.
| |
Collapse
|
2
|
Roshanravan B, Kestenbaum B, Gamboa J, Jubrias SA, Ayers E, Curtin L, Himmelfarb J, de Boer IH, Conley KE. CKD and Muscle Mitochondrial Energetics. Am J Kidney Dis 2016; 68:658-659. [PMID: 27312460 DOI: 10.1053/j.ajkd.2016.05.011] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 05/06/2016] [Indexed: 12/22/2022]
Affiliation(s)
- Baback Roshanravan
- University of Washington Kidney Research Institute, Seattle, Washington.
| | - Bryan Kestenbaum
- University of Washington Kidney Research Institute, Seattle, Washington
| | - Jorge Gamboa
- Vanderbilt University Medical Center, Nashville, Tennessee
| | | | - Ernest Ayers
- University of Washington Kidney Research Institute, Seattle, Washington
| | - Laura Curtin
- University of Washington Kidney Research Institute, Seattle, Washington
| | | | - Ian H de Boer
- University of Washington Kidney Research Institute, Seattle, Washington
| | | |
Collapse
|
3
|
Conley KE, Ali AS, Flores B, Jubrias SA, Shankland EG. Mitochondrial NAD(P)H In vivo: Identifying Natural Indicators of Oxidative Phosphorylation in the (31)P Magnetic Resonance Spectrum. Front Physiol 2016; 7:45. [PMID: 27065875 PMCID: PMC4812112 DOI: 10.3389/fphys.2016.00045] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 02/01/2016] [Indexed: 01/20/2023] Open
Abstract
Natural indicators provide intrinsic probes of metabolism, biogenesis and oxidative protection. Nicotinamide adenine dinucleotide metabolites (NAD(P)) are one class of indicators that have roles as co-factors in oxidative phosphorylation, glycolysis, and anti-oxidant protection, as well as signaling in the mitochondrial biogenesis pathway. These many roles are made possible by the distinct redox states (NAD(P)(+) and NAD(P)H), which are compartmentalized between cytosol and mitochondria. Here we provide evidence for detection of NAD(P)(+) and NAD(P)H in separate mitochondrial and cytosol pools in vivo in human tissue by phosphorus magnetic resonance spectroscopy ((31)P MRS). These NAD(P) pools are identified by chemical standards (NAD(+), NADP(+), and NADH) and by physiological tests. A unique resonance reflecting mitochondrial NAD(P)H is revealed by the changes elicited by elevation of mitochondrial oxidation. The decline of NAD(P)H with oxidation is matched by a stoichiometric rise in the NAD(P)(+) peak. This unique resonance also provides a measure of the improvement in mitochondrial oxidation that parallels the greater phosphorylation found after exercise training in these elderly subjects. The implication is that the dynamics of the mitochondrial NAD(P)H peak provides an intrinsic probe of the reversal of mitochondrial dysfunction in elderly muscle. Thus, non-invasive detection of NAD(P)(+) and NAD(P)H in cytosol vs. mitochondria yields natural indicators of redox compartmentalization and sensitive intrinsic probes of the improvement of mitochondrial function with an intervention in human tissues in vivo. These natural indicators hold the promise of providing mechanistic insight into metabolism and mitochondrial function in vivo in a range of tissues in health, disease and with treatment.
Collapse
Affiliation(s)
- Kevin E Conley
- Department of Radiology, University of Washington Medical CenterSeattle, WA, USA; Department of Physiology and Biophysics, University of Washington Medical CenterSeattle, WA, USA; Department of Bioengineering, University of Washington Medical CenterSeattle, WA, USA
| | - Amir S Ali
- Department of Radiology, University of Washington Medical Center Seattle, WA, USA
| | - Brandon Flores
- Department of Radiology, University of Washington Medical Center Seattle, WA, USA
| | - Sharon A Jubrias
- Department of Radiology, University of Washington Medical Center Seattle, WA, USA
| | - Eric G Shankland
- Department of Radiology, University of Washington Medical Center Seattle, WA, USA
| |
Collapse
|
4
|
Ortega JO, Lindstedt SL, Nelson FE, Jubrias SA, Kushmerick MJ, Conley KE. Muscle force, work and cost: a novel technique to revisit the Fenn effect. ACTA ACUST UNITED AC 2015; 218:2075-82. [PMID: 25964423 DOI: 10.1242/jeb.114512] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Accepted: 04/29/2015] [Indexed: 11/20/2022]
Abstract
Muscle produces force by forming cross-bridges, using energy released from ATP. While the magnitude and duration of force production primarily determine the energy requirement, nearly a century ago Fenn observed that muscle shortening or lengthening influenced energetic cost of contraction. When work is done by the muscle, the energy cost is increased and when work is done on the muscle the energy cost is reduced. However, the magnitude of the 'Fenn effect' and its mirror ('negative Fenn effect') have not been quantitatively resolved. We describe a new technique coupling magnetic resonance spectroscopy with an in vivo force clamp that can directly quantify the Fenn effect [E=I+W, energy liberated (E) equals the energy cost of isometric force production (I) plus the work done (W)] and the negative Fenn effect (E=I-W) for one muscle, the first dorsal interosseous (FDI). ATP cost was measured during a series of contractions, each of which occurred at a constant force and for a constant duration, thus constant force-time integral (FTI). In all subjects, as the FTI increased with load, there was a proportional linear increase in energy cost. In addition, the cost of producing force greatly increased when the muscle shortened, and was slightly reduced during lengthening contraction. These results, though limited to a single muscle, contraction velocity and muscle length change, do quantitatively support the Fenn effect. We speculate that they also suggest that an elastic element within the FDI muscle functions to preserve the force generated within the cross-bridges.
Collapse
Affiliation(s)
- Justus O Ortega
- Department of Kinesiology & Recreation Administration, Humboldt State University, Arcata, CA 95521, USA Department of Radiology, University of Washington Medical Center, Seattle, WA 98195, USA
| | - Stan L Lindstedt
- Department of Biological Sciences, Northern Arizona University, South Beaver Street, Flagstaff, AZ 86001, USA
| | - Frank E Nelson
- Department of Radiology, University of Washington Medical Center, Seattle, WA 98195, USA
| | - Sharon A Jubrias
- Department of Radiology, University of Washington Medical Center, Seattle, WA 98195, USA
| | - Martin J Kushmerick
- Department of Radiology, University of Washington Medical Center, Seattle, WA 98195, USA
| | - Kevin E Conley
- Department of Radiology, University of Washington Medical Center, Seattle, WA 98195, USA Department of Physiology & Biophysics, University of Washington Medical Center, Seattle, WA 98195, USA Department of Bioengineering, University of Washington Medical Center, Seattle, WA 98105, USA
| |
Collapse
|
5
|
Santanasto AJ, Glynn NW, Jubrias SA, Conley KE, Boudreau RM, Amati F, Mackey DC, Simonsick EM, Strotmeyer ES, Coen PM, Goodpaster BH, Newman AB. Skeletal Muscle Mitochondrial Function and Fatigability in Older Adults. J Gerontol A Biol Sci Med Sci 2014; 70:1379-85. [PMID: 25167867 DOI: 10.1093/gerona/glu134] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Accepted: 06/28/2014] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Fatigability increases while the capacity for mitochondrial energy production tends to decrease significantly with age. Thus, diminished mitochondrial function may contribute to higher levels of fatigability in older adults. METHODS The relationship between fatigability and skeletal muscle mitochondrial function was examined in 30 participants aged 78.5 ± 5.0 years (47% female, 93% white), with a body mass index of 25.9 ± 2.7 kg/m(2) and usual gait-speed of 1.2 ± 0.2 m/s. Fatigability was defined using rating of perceived exertion (6-20 point Borg scale) after a 5-minute treadmill walk at 0.72 m/s. Phosphocreatine recovery in the quadriceps was measured using (31)P magnetic resonance spectroscopy and images of the quadriceps were captured to calculate quadriceps volume. ATPmax (mM ATP/s) and oxidative capacity of the quadriceps (ATPmax·Quadriceps volume) were calculated. Peak aerobic capacity (VO2peak) was measured using a modified Balke protocol. RESULTS ATPmax·Quadriceps volume was associated with VO2peak and was 162.61mM ATP·mL/s lower (p = .03) in those with high (rating of perceived exertion ≥10) versus low (rating of perceived exertion ≤9) fatigability. Participants with high fatigability required a significantly higher proportion of VO2peak to walk at 0.72 m/s compared with those with low fatigability (58.7 ± 19.4% vs 44.9 ± 13.2%, p < .05). After adjustment for age and sex, higher ATPmax was associated with lower odds of having high fatigability (odds ratio: 0.34, 95% CI: 0.11-1.01, p = .05). CONCLUSIONS Lower capacity for oxidative phosphorylation in the quadriceps, perhaps by contributing to lower VO2peak, is associated with higher fatigability in older adults.
Collapse
Affiliation(s)
- Adam J Santanasto
- Department of Epidemiology, Center for Aging and Population Health, Graduate School of Public Health, University of Pittsburgh, Pennsylvania
| | - Nancy W Glynn
- Department of Epidemiology, Center for Aging and Population Health, Graduate School of Public Health, University of Pittsburgh, Pennsylvania.
| | - Sharon A Jubrias
- Translational Center for Metabolic Imaging, University of Washington, Seattle
| | - Kevin E Conley
- Translational Center for Metabolic Imaging, University of Washington, Seattle
| | - Robert M Boudreau
- Department of Epidemiology, Center for Aging and Population Health, Graduate School of Public Health, University of Pittsburgh, Pennsylvania
| | - Francesca Amati
- Division of Endocrinology and Metabolism, School of Medicine, University of Pittsburgh, Pennsylvania
| | - Dawn C Mackey
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
| | - Eleanor M Simonsick
- Translational Gerontology Branch, National Institute on Aging, Baltimore, Maryland
| | - Elsa S Strotmeyer
- Department of Epidemiology, Center for Aging and Population Health, Graduate School of Public Health, University of Pittsburgh, Pennsylvania
| | - Paul M Coen
- Division of Endocrinology and Metabolism, School of Medicine, University of Pittsburgh, Pennsylvania. Department of Health and Physical Activity, School of Education, University of Pittsburgh, Pennsylvania. Present address: Florida Hospital-Sanford
- Burnham Translational Research Institute for Metabolism and Diabetes, Orlando
| | - Bret H Goodpaster
- Division of Endocrinology and Metabolism, School of Medicine, University of Pittsburgh, Pennsylvania. Present address: Florida Hospital-Sanford
- Burnham Translational Research Institute for Metabolism and Diabetes, Orlando
| | - Anne B Newman
- Department of Epidemiology, Center for Aging and Population Health, Graduate School of Public Health, University of Pittsburgh, Pennsylvania
| |
Collapse
|
6
|
Conley KE, Amara CE, Bajpeyi S, Costford SR, Murray K, Jubrias SA, Arakaki L, Marcinek DJ, Smith SR. Higher mitochondrial respiration and uncoupling with reduced electron transport chain content in vivo in muscle of sedentary versus active subjects. J Clin Endocrinol Metab 2013; 98:129-36. [PMID: 23150693 PMCID: PMC3537085 DOI: 10.1210/jc.2012-2967] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
OBJECTIVE This study investigated the disparity between muscle metabolic rate and mitochondrial metabolism in human muscle of sedentary vs. active individuals. RESEARCH DESIGN AND METHODS Chronic activity level was characterized by a physical activity questionnaire and a triaxial accelerometer as well as a maximal oxygen uptake test. The ATP and O(2) fluxes and mitochondrial coupling (ATP/O(2) or P/O) in resting muscle as well as mitochondrial capacity (ATP(max)) were determined in vivo in human vastus lateralis muscle using magnetic resonance and optical spectroscopy on 24 sedentary and seven active subjects. Muscle biopsies were analyzed for electron transport chain content (using complex III as a representative marker) and mitochondrial proteins associated with antioxidant protection. RESULTS Sedentary muscle had lower electron transport chain complex content (65% of the active group) in proportion to the reduction in ATP(max) (0.69 ± 0.07 vs. 1.07 ± 0.06 mM sec(-1)) as compared with active subjects. This lower ATP(max) paired with an unchanged O(2) flux in resting muscle between groups resulted in a doubling of O(2) flux per ATP(max) (3.3 ± 0.3 vs. 1.7 ± 0.2 μM O(2) per mM ATP) that reflected mitochondrial uncoupling (P/O = 1.41 ± 0.1 vs. 2.1 ± 0.3) and greater UCP3/complex III (6.0 ± 0.7 vs. 3.8 ± 0.3) in sedentary vs. active subjects. CONCLUSION A smaller mitochondrial pool serving the same O(2) flux resulted in elevated mitochondrial respiration in sedentary muscle. In addition, uncoupling contributed to this higher mitochondrial respiration. This finding resolves the paradox of stable muscle metabolism but greater mitochondrial respiration in muscle of inactive vs. active subjects.
Collapse
Affiliation(s)
- Kevin E Conley
- Department of Radiology, University of Washington Medical Center, Box 357115, Seattle, Washington 98195-7115, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Conley KE, Jubrias SA, Cress ME, Esselman PC. Elevated energy coupling and aerobic capacity improves exercise performance in endurance-trained elderly subjects. Exp Physiol 2012. [PMID: 23204291 DOI: 10.1113/expphysiol.2012.069633] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Increased maximal oxygen uptake (V(O(2)max)), mitochondrial capacity and energy coupling efficiency are reported after endurance training (ET) in adult subjects. Here we test whether leg exercise performance (power output of the legs, P(max), at V(O(2)max)) reflects these improvements with ET in the elderly. Fifteen male and female subjects were endurance trained for a 6 month programme, with 13 subjects (69.5 ± 1.2 years old, range 65-80 years old; n = 7 males; n = 6 females) completing the study. This training significantly improved P(max) (Δ17%; P = 0.003), V(O(2)max) (Δ5.4%; P = 0.021) and the increment in oxygen uptake (V(O(2))) above resting (ΔV(O(2)m-r) = V(O(2)max) - V(O(2)rest; Δ9%; P < 0.02). In addition, evidence of improved energy coupling came from elevated leg power output per unit V(O(2))at the aerobic capacity [Δ(P(max)/ΔV(O(2)m-r)); P = 0.02] and during submaximal exercise in the ramp test as measured by delta efficiency (ΔP(ex)/ΔV(O(2)); P = 0.04). No change was found in blood lactate, muscle glycolysis or fibre type. The rise in P(max) paralleled the improvement in muscle oxidative phosphorylation capacity (ATP(max)) in these subjects. In addition, the greater exercise energy coupling [Δ(P(max)/ΔV(O(2)m-r)) and delta efficiency] was accompanied by increased mitochondrial energy coupling as measured by elevated ATP production per unit mitochondrial content in these subjects. These results suggest that leg exercise performance benefits from elevations in energy coupling and oxidative phosphorylation capacity at both the whole-body and muscle levels that accompany endurance training in the elderly.
Collapse
Affiliation(s)
- Kevin E Conley
- Department of Radiology, Box 357115, University of Washington Medical Center, Seattle, WA 98195-7115, USA.
| | | | | | | |
Collapse
|
8
|
Abstract
A reduction in exercise efficiency accompanies ageing in humans. Here we evaluated the impact of changes in the contractile-coupling and mitochondrial-coupling efficiencies on the reduction in exercise efficiency in the elderly. Nine adult (mean, 38.8 years old) and 40 elderly subjects (mean, 68.8 years old) performed a cycle ergometer test to measure O2 uptake and leg power output up to the aerobic limit ( ). Reduced leg power output per unit O2 uptake was reflected in a drop in delta efficiency (εD) from 0.27 ± 0.01 (mean ± SEM) in adults to 0.22 ± 0.01 in the elderly group. Similar declines with age were apparent for both the leg power output at and the ATP generation capacity (ATPmax) determined in vivo using (31)P magnetic resonance spectroscopy. These similar declines resulted in unchanged contractile-coupling efficiency values (εC) in the adult (0.50 ± 0.05) versus the elderly group (0.58 ± 0.04) and agreed with independent measures of muscle contractile-coupling efficiency in human quadriceps (0.5). The mitochondrial-coupling efficiency calculated from the ratio of delta to contractile-coupling efficiencies in the adults (εD/εC = 0.58 ± 0.08) corresponded to values for well-coupled mitochondria (0.6); however, εD/εC was significantly lower in the elderly subjects (0.44 ± 0.03). Conversion of ATPmax per mitochondrial volume (ATPmax/Vv[mt,f]) reported in these groups into thermodynamic units confirmed this drop in mitochondrial-coupling efficiency from 0.57 ± 0.08 in adults to 0.41 ± 0.03 in elderly subjects. Thus, two independent methods revealed that reduced mitochondrial-coupling efficiency was a key part of the drop in exercise efficiency in these elderly subjects and may be an important part of the loss of exercise performance with age.
Collapse
Affiliation(s)
- Kevin E Conley
- Department of Radiology, Box 357115, University of Washington Medical Center, Seattle, WA 98195-7115, USA.
| | | | | | | |
Collapse
|
9
|
Coen PM, Jubrias SA, Distefano G, Amati F, Mackey DC, Glynn NW, Manini TM, Wohlgemuth SE, Leeuwenburgh C, Cummings SR, Newman AB, Ferrucci L, Toledo FGS, Shankland E, Conley KE, Goodpaster BH. Skeletal muscle mitochondrial energetics are associated with maximal aerobic capacity and walking speed in older adults. J Gerontol A Biol Sci Med Sci 2012; 68:447-55. [PMID: 23051977 DOI: 10.1093/gerona/gls196] [Citation(s) in RCA: 217] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Lower ambulatory performance with aging may be related to a reduced oxidative capacity within skeletal muscle. This study examined the associations between skeletal muscle mitochondrial capacity and efficiency with walking performance in a group of older adults. METHODS Thirty-seven older adults (mean age 78 years; 21 men and 16 women) completed an aerobic capacity (VO2 peak) test and measurement of preferred walking speed over 400 m. Maximal coupled (State 3; St3) mitochondrial respiration was determined by high-resolution respirometry in saponin-permeabilized myofibers obtained from percutanous biopsies of vastus lateralis (n = 22). Maximal phosphorylation capacity (ATPmax) of vastus lateralis was determined in vivo by (31)P magnetic resonance spectroscopy (n = 30). Quadriceps contractile volume was determined by magnetic resonance imaging. Mitochondrial efficiency (max ATP production/max O2 consumption) was characterized using ATPmax per St3 respiration (ATPmax/St3). RESULTS In vitro St3 respiration was significantly correlated with in vivo ATPmax (r (2) = .47, p = .004). Total oxidative capacity of the quadriceps (St3*quadriceps contractile volume) was a determinant of VO2 peak (r (2) = .33, p = .006). ATPmax (r (2) = .158, p = .03) and VO2 peak (r (2) = .475, p < .0001) were correlated with preferred walking speed. Inclusion of both ATPmax/St3 and VO2 peak in a multiple linear regression model improved the prediction of preferred walking speed (r (2) = .647, p < .0001), suggesting that mitochondrial efficiency is an important determinant for preferred walking speed. CONCLUSIONS Lower mitochondrial capacity and efficiency were both associated with slower walking speed within a group of older participants with a wide range of function. In addition to aerobic capacity, lower mitochondrial capacity and efficiency likely play roles in slowing gait speed with age.
Collapse
Affiliation(s)
- Paul M Coen
- Department of Health and Physical Activity, University of Pittsburgh, Trees Hall Rm 134D, Allequippa St. and Darragh St., Pittsburgh, PA 15260, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Abstract
Can human muscle be highly efficient in vivo? Animal muscles typically show contraction-coupling efficiencies <50% in vitro but a recent study reports that the human first dorsal interosseous (FDI) muscle of the hand has an efficiency value in vivo of 68%. We examine two key factors that could account for this apparently high efficiency value: (1) transfer of cross-bridge work into mechanical work and (2) the use of elastic energy to do external work. Our analysis supports a high contractile efficiency reflective of nearly complete transfer of muscular to mechanical work with no contribution by recycling of elastic energy to mechanical work. Our survey of reported contraction-coupling efficiency values puts the FDI value higher than typical values found in small animals in vitro but within the range of values for human muscle in vivo. These high efficiency values support recent studies that suggest lower Ca(2+) cycling costs in working contractions and a decline in cost during repeated contractions. In the end, our analysis indicates that the FDI muscle may be exceptional in having an efficiency value on the higher end of that reported for human muscle. Thus, the FDI muscle may be an exception both in contraction-coupling efficiency and in Ca(2+) cycling costs, which makes it an ideal muscle model system offering prime conditions for studying the energetics of muscle contraction in vivo.
Collapse
|
11
|
Ortega J, Nelson F, Linstedt SL, Jubrias SA, Kushmerick MJ, Conley KE. An innovative apparatus for measuring in vivo efficiency of positive and negative work for human muscle studies. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.1051.32] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
12
|
Nelson FE, Ortega JD, Linstedt SL, Jubrias SA, Kushmerick MJ, Conley KE. Does negative work cost less. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.1051.25] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
13
|
Costford SR, Bajpeyi S, Pasarica M, Albarado DC, Thomas SC, Xie H, Church TS, Jubrias SA, Conley KE, Smith SR. Skeletal muscle NAMPT is induced by exercise in humans. Am J Physiol Endocrinol Metab 2010; 298:E117-26. [PMID: 19887595 PMCID: PMC2806106 DOI: 10.1152/ajpendo.00318.2009] [Citation(s) in RCA: 189] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
In mammals, nicotinamide phosphoribosyltransferase (NAMPT) is responsible for the first and rate-limiting step in the conversion of nicotinamide to nicotinamide adenine dinucleotide (NAD+). NAD+ is an obligate cosubstrate for mammalian sirtuin-1 (SIRT1), a deacetylase that activates peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), which in turn can activate mitochondrial biogenesis. Given that mitochondrial biogenesis is activated by exercise, we hypothesized that exercise would increase NAMPT expression, as a potential mechanism leading to increased mitochondrial content in muscle. A cross-sectional analysis of human subjects showed that athletes had about a twofold higher skeletal muscle NAMPT protein expression compared with sedentary obese, nonobese, and type 2 diabetic subjects (P < 0.05). NAMPT protein correlated with mitochondrial content as estimated by complex III protein content (R(2) = 0.28, P < 0.01), MRS-measured maximal ATP synthesis (R(2) = 0.37, P = 0.002), and Vo(2max) (R(2) = 0.63, P < 0.0001). In an exercise intervention study, NAMPT protein increased by 127% in sedentary nonobese subjects after 3 wk of exercise training (P < 0.01). Treatment of primary human myotubes with forskolin, a cAMP signaling pathway activator, resulted in an approximately 2.5-fold increase in NAMPT protein expression, whereas treatment with ionomycin had no effect. Activation of AMPK via AICAR resulted in an approximately 3.4-fold increase in NAMPT mRNA (P < 0.05) as well as modest increases in NAMPT protein (P < 0.05) and mitochondrial content (P < 0.05). These results demonstrate that exercise increases skeletal muscle NAMPT expression and that NAMPT correlates with mitochondrial content. Further studies are necessary to elucidate the pathways regulating NAMPT as well as its downstream effects.
Collapse
Affiliation(s)
- Sheila R Costford
- Pennington Biomedical Research Center, 6400 Perkins Rd., Baton Rouge, LA 70808, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
14
|
Conley KE, Jubrias SA, Cress ME, Esselman P. Mitochondrial Dysfunction Impacts Exercise Efficiency In The Elderly. Med Sci Sports Exerc 2009. [DOI: 10.1249/01.mss.0000353455.37318.9e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
15
|
Conley KE, Jubrias SA, Shankland E, Amara CE, Marcinek DJ. Does Mitochondrial Uncoupling Generate More Mitochondria in Muscle? FASEB J 2009. [DOI: 10.1096/fasebj.23.1_supplement.600.30] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
16
|
Jubrias SA, Vollestad NK, Gronka RK, Kushmerick MJ. Contraction coupling efficiency of human first dorsal interosseous muscle. J Physiol 2008; 586:1993-2002. [PMID: 18238810 PMCID: PMC2375725 DOI: 10.1113/jphysiol.2007.146829] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 10/17/2007] [Accepted: 01/30/2008] [Indexed: 11/08/2022] Open
Abstract
During working contractions, chemical energy in the form of ATP is converted to external work. The efficiency of this conversion, called 'contraction coupling efficiency', is calculated by the ratio of work output to energy input from ATP splitting. Experiments on isolated muscles and permeabilized fibres show the efficiency of this conversion has a wide range, 0.2-0.7. We measured the work output in contractions of a single human hand muscle in vivo and of the ATP cost of that work to calculate the contraction coupling efficiency of the muscle. Five subjects performed six bouts of rapid voluntary contractions every 1.5 s for 42 s (28 contractions, each with time to peak force < 150 ms). The bouts encompassed a 7-fold range of workloads. The ATP cost during work was quantified by measuring the extent of chemical changes within the muscle from (31)P magnetic resonance spectra. Contraction coupling efficiency was determined as the slope of paired measurements of work output and ATP cost at the five graded work loads. The results show that 0.68 of the chemical energy available from ATP splitting was converted to external work output. A plausible mechanism to account for this high value is a substantially lower efficiency for mitochondrial ATP synthesis. The method described here can be used to analyse changes in the overall efficiency determined from oxygen consumption during exercise that can occur in disease or with age, and to test the hypothesis that such changes are due to reduced contraction coupling efficiency.
Collapse
Affiliation(s)
- Sharon A Jubrias
- Department of Radiology, University of Washington, Seattle, WA, USA.
| | | | | | | |
Collapse
|
17
|
Abstract
Innovative noninvasive methods open a new window on the cell in vivo. This window reveals that the tempo of mitochondrial dysfunction with age varies among muscles and in proportion to Type II muscle fiber content. Exercise training can reverse age-related dysfunction, thereby providing an intervention to slow the pace of aging and disability in the elderly.
Collapse
Affiliation(s)
- Kevin E Conley
- Department of Radiology, University of Washington Medical Center, Seattle, WA 98195-7115, USA.
| | | | | | | |
Collapse
|
18
|
Amara CE, Shankland EG, Jubrias SA, Marcinek DJ, Kushmerick MJ, Conley KE. Mild mitochondrial uncoupling impacts cellular aging in human muscles in vivo. Proc Natl Acad Sci U S A 2007; 104:1057-62. [PMID: 17215370 PMCID: PMC1766336 DOI: 10.1073/pnas.0610131104] [Citation(s) in RCA: 168] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Faster aging is predicted in more active tissues and animals because of greater reactive oxygen species generation. Yet age-related cell loss is greater in less active cell types, such as type II muscle fibers. Mitochondrial uncoupling has been proposed as a mechanism that reduces reactive oxygen species production and could account for this paradox between longevity and activity. We distinguished these hypotheses by using innovative optical and magnetic resonance spectroscopic methods applied to noninvasively measured ATP synthesis and O(2) uptake in vivo in human muscle. Here we show that mitochondrial function is unchanged with age in mildly uncoupled tibialis anterior muscle (75% type I) despite a high respiratory rate in adults. In contrast, substantial uncoupling and loss of cellular [ATP] indicative of mitochondrial dysfunction with age was found in the lower respiring and well coupled first dorsal interosseus (43-50% type II) of the same subjects. These results reject respiration rate as the sole factor impacting the tempo of cellular aging. Instead, they support mild uncoupling as a mechanism protecting mitochondrial function and contributing to the paradoxical longevity of the most active muscle fibers.
Collapse
Affiliation(s)
| | | | | | | | - Martin J. Kushmerick
- Departments of *Radiology
- Physiology and Biophysics, and
- Bioengineering, University of Washington Medical Center, Seattle, WA 98195
| | - Kevin E. Conley
- Departments of *Radiology
- Physiology and Biophysics, and
- Bioengineering, University of Washington Medical Center, Seattle, WA 98195
- To whom correspondence should be addressed at:
Department of Radiology, Box 357115, University of Washington Medical Center, Seattle, WA 98195-7115. E-mail:
| |
Collapse
|
19
|
Abstract
Mitochondrial changes are at the centre of a wide range of maladies, including diabetes, neurodegeneration and ageing-related dysfunctions. Here we describe innovative optical and magnetic resonance spectroscopic methods that non-invasively measure key mitochondrial fluxes, ATP synthesis and O(2) uptake, to permit the determination of mitochondrial coupling efficiency in vivo (P/O: half the ratio of ATP flux to O(2) uptake). Three new insights result. First, mitochondrial coupling can be measured in vivo with the rigor of a biochemical determination and provides a gold standard to define well-coupled mitochondria (P/O approximately 2.5). Second, mitochondrial coupling differs substantially among muscles in healthy adults, from values reflective of well-coupled oxidative phosphorylation in a hand muscle (P/O = 2.7) to mild uncoupling in a leg muscle (P/O = 2.0). Third, these coupling differences have an important impact on cell ageing. We found substantial uncoupling and loss of cellular [ATP] in a hand muscle indicative of mitochondrial dysfunction with age. In contrast, stable mitochondrial function was found in a leg muscle, which supports the notion that mild uncoupling is protective against mitochondrial damage with age. Thus, greater mitochondrial dysfunction is evident in muscles with higher type II muscle fibre content, which may be at the root of the preferential loss of type II fibres found in the elderly. Our results demonstrate that mitochondrial function and the tempo of ageing varies among human muscles in the same individual. These technical advances, in combination with the range of mitochondrial properties available in human muscles, provide an ideal system for studying mitochondrial function in normal tissue and the link between mitochondrial defects and cell pathology in disease.
Collapse
Affiliation(s)
- Kevin E Conley
- Department of Radiology, Box 357115, University of Washington Medical Center, Seattle, WA 98195-7115, USA.
| | | | | | | |
Collapse
|
20
|
Amara CE, Jubrias SA, Marcinek DJ, Kushmerick MJ, Conley KE. Mitochondrial Energy Coupling (ATP/O2) In Human Muscle. Med Sci Sports Exerc 2005. [DOI: 10.1249/00005768-200505001-02355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
21
|
Abstract
This study tested the hypothesis that acidic pH inhibits oxidative ATP supply during exercise in hand (first dorsal interosseus, FDI) and lower limb (leg anterior compartment, LEG) muscles. We measured oxidative flux and estimated mitochondrial capacity using the changes in creatine phosphate concentration ([PCr]) and pH as detected by 31P magnetic resonance (MR) spectroscopy during isometric exercise and recovery. The highest oxidative ATP flux in sustained exercise was about half the estimated mitochondrial capacity in the LEG (0.38 +/- 0.06 vs. 0.90 +/- 0.14 mM ATP s(-1), respectively), but at the estimated capacity in the FDI (0.61 +/- 0.05 vs. 0.61 +/- 0.09 mM ATP s(-1), respectively). During sustained exercise at a higher contraction rate, intracellular acidosis (pH < 6.88) prevented a rise in oxidative flux in the LEG and FDI despite significantly increased [ADP]. We tested whether oxidative flux could increase above that achieved in sustained exercise by raising [ADP] (> 0.24 mM) and avoiding acidosis using burst exercise. This exercise raised oxidative flux (0.69 +/- 0.05 mM ATP s(-1)) to nearly twice that found with sustained exercise in the LEG and matched (0.65 +/- 0.11 mM ATP s(-1)) the near maximal flux seen during sustained exercise in the FDI. Thus both muscles reached their highest oxidative fluxes in the absence of acidosis. These results show that acidosis inhibits oxidative phosphorylation in vivo and can limit ATP supply in exercising muscle to below the mitochondrial capacity.
Collapse
Affiliation(s)
- Sharon A Jubrias
- Department of Radiology, University of Washington Medical Center, Seattle, WA 98195, USA
| | | | | | | | | |
Collapse
|
22
|
Crowther GJ, Milstein JM, Jubrias SA, Kushmerick MJ, Gronka RK, Conley KE. Altered energetic properties in skeletal muscle of men with well-controlled insulin-dependent (type 1) diabetes. Am J Physiol Endocrinol Metab 2003; 284:E655-62. [PMID: 12626321 DOI: 10.1152/ajpendo.00343.2002] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
This study asked whether the energetic properties of muscles are changed by insulin-dependent diabetes mellitus (or type 1 diabetes), as occurs in obesity and type 2 diabetes. We used (31)P magnetic resonance spectroscopy to measure glycolytic flux, oxidative flux, and contractile cost in the ankle dorsiflexor muscles of 10 men with well-managed type 1 diabetes and 10 age- and activity-matched control subjects. Each subject performed sustained isometric muscle contractions lasting 30 and 120 s while attempting to maintain 70-75% of maximal voluntary contraction force. An altered glycolytic flux in type 1 diabetic subjects relative to control subjects was apparent from significant differences in pH in muscle at rest and at the end of the 120-s bout. Glycolytic flux during exercise began earlier and reached a higher peak rate in diabetic patients than in control subjects. A reduced oxidative capacity in the diabetic patients' muscles was evident from a significantly slower phosphocreatine recovery from a 30-s exercise bout. Our findings represent the first characterization of the energetic properties of muscle from type 1 diabetic patients. The observed changes in glycolytic and oxidative fluxes suggest a diabetes-induced shift in the metabolic profile of muscle, consistent with studies of obesity and type 2 diabetes that point to common muscle adaptations in these diseases.
Collapse
Affiliation(s)
- Gregory J Crowther
- Department of Physiology and Biophysics, University of Washington Medical Center, Seattle 98195, USA
| | | | | | | | | | | |
Collapse
|
23
|
Abstract
PURPOSE Fast- and slow-twitch human muscle fibers exhibit large (two- to threefold) differences in metabolic enzyme activities and contractile economy. We asked whether comparable flux differences are evident in the muscles of athletes specializing in extremely different (i.e., sprint and long-distance) running events. METHODS We took an in vivo "functional biopsy" of the ankle dorsiflexor muscles of 17 members of a university track team by using (31)P magnetic resonance spectroscopy. Ten sprinters (SPR) and seven distance runners (DIS) performed rapid isometric dorsiflexions against the resistance of a plastic foot holder. The contractile cost of exercise and glycolytic flux were calculated from changes in pH, [PCr], and [P(i)] during ischemic exercise, and oxidative capacity was calculated from PCr recovery kinetics after aerobic exercise. RESULTS Contractile costs were 47% higher in SPR than in DIS, whereas oxidative capacities were 52% higher in DIS than in SPR. Surprisingly, glycolytic ATP production was similar in the two groups. CONCLUSION The muscles of SPR and DIS exhibit clear differences in energetic properties, but these differences are smaller than the two- to three-fold variations seen in the properties of individual muscle fibers.
Collapse
Affiliation(s)
- Gregory J Crowther
- Department of Radiology, University of Washington Medical Center, Seattle, 98195-7115, USA
| | | | | | | |
Collapse
|
24
|
Abstract
This study determined the cellular energetic and structural adaptations of elderly muscle to exercise training. Forty male and female subjects (69.2 +/- 0.6 yr) were assigned to a control group or 6 mo of endurance (ET) or resistance training (RT). We used magnetic resonance spectroscopy and imaging to characterize energetic properties and size of the quadriceps femoris muscle. The phosphocreatine and pH changes during exercise yielded the muscle oxidative properties, glycolytic ATP synthesis, and contractile ATP demand. Muscle biopsies taken from the same site as the magnetic resonance measurements were used to determine myosin heavy chain isoforms, metabolite concentrations, and mitochondrial volume densities. The ET group showed changes in all energetic pathways: oxidative capacity (+31%), contractile ATP demand (-21%), and glycolytic ATP supply (-56%). The RT group had a large increase in oxidative capacity (57%). Only the RT group exhibited change in structural properties: a rise in mitochondrial volume density (31%) and muscle size (10%). These results demonstrate large energetic, but smaller structural, adaptations by elderly muscle with exercise training. The rise in oxidative properties with both ET and RT suggests that the aerobic pathway is particularly sensitive to exercise training in elderly muscle. Thus elderly muscle remains adaptable to chronic exercise, with large energetic changes accompanying both ET and RT.
Collapse
Affiliation(s)
- S A Jubrias
- Department of Radiology, University of Washington, Seattle, Washington 98195, USA.
| | | | | | | | | |
Collapse
|
25
|
Abstract
This paper asks how the decline in maximal O(2) uptake rate (VO(2),max) with age is related to the properties of a key muscle group involved in physical activity - the quadriceps muscles. Maximal oxygen consumption on a cycle ergometer was examined in nine adult (mean age 38.8 years) and 39 elderly subjects (mean age 68.8 years) and compared with the oxidative capacity and volume of the quadriceps. VO(2),max declined with age between 25 and 80 years and the increment in oxygen consumption from unloaded cycling to VO(2),max (delta VO(2)) in the elderly was 45 % of the adult value. The cross-sectional areas of the primary muscles involved in cycling - the hamstrings, gluteus maximus and quadriceps - were all lower in the elderly group. The quadriceps volume was reduced in the elderly to 67 % of the adult value. Oxidative capacity per quadriceps volume was reduced to 53 % of the adult value. The product of oxidative capacity and muscle volume - the quadriceps oxidative capacity - was 36 % of the adult value in the elderly. Quadriceps oxidative capacity was linearly correlated with delta VO(2) among the subjects with the slope indicating that the quadriceps represented 36 % of the VO(2) increase during cycling. The decline in quadriceps oxidative capacity with age resulted from reductions in both muscle volume and oxidative capacity per volume in the elderly and appears to be an important determinant of the age-related reduction in delta VO(2) and VO(2),max found in this study.
Collapse
Affiliation(s)
- K E Conley
- Department of Radiology, University of Washington Medical Center, Seattle, WA 98195-7115,
| | | | | | | | | | | | | |
Collapse
|
26
|
Abstract
This study determined the decline in oxidative capacity per volume of human vastus lateralis muscle between nine adult (mean age 38.8 years) and 40 elderly (mean age 68.8 years) human subjects (age range 25-80 years). We based our oxidative capacity estimates on the kinetics of changes in creatine phosphate content ([PCr]) during recovery from exercise as measured by (31)P magnetic resonance (MR) spectroscopy. A matched muscle biopsy sample permitted determination of mitochondrial volume density and the contribution of the loss of mitochondrial content to the decline in oxidative capacity with age. The maximal oxidative phosphorylation rate or oxidative capacity was estimated from the PCr recovery rate constant (k(PCr)) and the [PCr] in accordance with a simple electrical circuit model of mitochondrial respiratory control. Oxidative capacity was 50 % lower in the elderly vs. the adult group (0.61 +/- 0.04 vs. 1.16 +/- 0.147 mM ATP s(-1)). Mitochondrial volume density was significantly lower in elderly compared with adult muscle (2.9 +/- 0.15 vs. 3.6 +/- 0.11 %). In addition, the oxidative capacity per mitochondrial volume (0.22 +/- 0.042 vs. 0.32 +/- 0.015 mM ATP (s %)(-1)) was reduced in elderly vs. adult subjects. This study showed that elderly subjects had nearly 50 % lower oxidative capacity per volume of muscle than adult subjects. The cellular basis of this drop was a reduction in mitochondrial content, as well as a lower oxidative capacity of the mitochondria with age.
Collapse
Affiliation(s)
- K E Conley
- Department of Radiology, University of Washington Medical Center, Seattle, WA 98195-7115, USA.
| | | | | |
Collapse
|
27
|
Abstract
1. We tested the hypothesis that the cytoplasmic control mechanism for glycolysis is affected by the presence of oxygen during exercise. We used a comparison of maximal twitch stimulation under ischaemic and intact circulation in human wrist flexor and ankle dorsiflexor muscles. 31P magnetic resonance spectroscopy followed the phosphocreatine (PCr), Pi and pH dynamics at 6-9 s intervals. Glycolytic PCr synthesis was determined during stimulation from pH and tissue buffer capacity, as well as the oxidative phosphorylation rate. 2. Ischaemic vs. aerobic stimulation resulted in similar glycolytic fluxes in the two muscles. The onset of glycolysis occured after fifty to seventy stimulations and the extent of glycolytic PCr synthesis was directly proportional to the number of stimulations thereafter. 3. Two-fold differences in the putative feedback regulators of glycolysis, [Pi] and [ADP], were found between aerobic and ischaemic stimulation. The similar glycolytic fluxes in the face of these differences in metabolite levels eliminates feedback as a control mechanism in glycolysis. 4. These results demonstrate that glycolytic flux is independent of oxygenation state and metabolic feedback, but proportional to muscle activation. These results show a key role for muscle stimulation in the activation and maintenance of glycolysis. Further, this glycolytic control mechanism is independent of the feedback control mechanism that governs oxidative phosphorylation.
Collapse
Affiliation(s)
- K E Conley
- Department of Radiology, University of Washington Medical Center, Seattle, WA 98195-7115, USA.
| | | | | |
Collapse
|
28
|
Abstract
We tested the cytoplasmic control mechanisms for glycolytic ATP synthesis in human wrist flexor muscles. The forearm was made ischemic and activated by maximal twitch stimulation of the median and ulnar nerves in 10 subjects. Kinetic changes in phosphocreatine, Pi, ADP, ATP, sugar phosphates, and pH were measured by 31P magnetic resonance spectroscopy at 7.1-s intervals. Proton production was determined from pH and tissue buffer capacity during stimulation. Glycolysis was activated between 30 and 50 stimulations, and the rate did not significantly change through the stimulation period. The independence of glycolytic rate on [Pi], [ADP], or [AMP] indicates that feedback regulation by these metabolites could not account for this activation of glycolysis. However, glycolytic H+ and ATP production increased sixfold from 0.5 to 3 Hz, indicating that glycolytic rate reflected muscle activation frequency. This dependence of glycolytic rate on muscle stimulation frequency and independence on metabolite levels is consistent with control of glycolysis by Ca2+.
Collapse
Affiliation(s)
- K E Conley
- Department of Radiology, University of Washington Medical Center, Seattle 98195, USA
| | | | | | | | | |
Collapse
|
29
|
Abstract
Humans produce less muscle force (F) as they age. However, the relationship between decreased force and muscle cross-sectional area (CSA) in older humans is not well documented. We examined changes in F and CSA to determine the relative contributions of muscle atrophy and specific force (F/CSA) to declining force production in aging humans. The proportions of myosin heavy chain (MHC) isoforms were characterized to assess whether this was related to changes in specific force with age. We measured the peak force of isokinetic knee extension in 57 males and females aged 23-80 years, and used magnetic resonance imaging to determine the contractile area of the quadriceps muscle. Analysis of MHC isoforms taken from biopsies of the vastus lateralis muscle showed no relation to specific force. F, CSA, and F/CSA decreased with age. Smaller CSA accounted for only about half of the 39% drop in force that occurred between ages 65-80 years. Specific force dropped about 1.5% per year in this age range, for a total decrease of 21%. Thus, quantitative changes in muscle (atrophy) are not sufficient to explain the strength loss associated with aging.
Collapse
Affiliation(s)
- S A Jubrias
- Department of Radiology, University of Washington Medical Center, Box 357115, Seattle WA 98195, USA
| | | | | | | |
Collapse
|
30
|
Abstract
Our goal is to show how muscle properties can be used to understand the exercise performance limitations of the elderly. We show that magnetic resonance (MR) imaging and spectroscopy are useful for noninvasively characterizing the structural and energetic properties of muscle in vivo. Determination of muscle volume and cross-sectional area is easily and rapidly accomplished by applying quantitative morphometric methods to MR images. New MR spectroscopic techniques provide a noninvasive "biopsy" of the oxidative, glycolytic, and contractile capacities of muscle fibers. We show how the structural and energetic properties measured by MR can be used to define the functional capacity of muscle and the contribution of this capacity to the performance of the whole body (e.g., VO2max). Finally, we relate these laboratory measures of muscle properties and performance to activities meaningful to the functioning of the elderly in everyday life, such as sustained walking and stair climbing.
Collapse
Affiliation(s)
- K E Conley
- Department of Radiology, University of Washington Medical Center, Seattle, USA
| | | | | | | | | |
Collapse
|
31
|
Jubrias SA, Bennett RM, Klug GA. Increased incidence of a resonance in the phosphodiester region of 31P nuclear magnetic resonance spectra in the skeletal muscle of fibromyalgia patients. Arthritis Rheum 1994; 37:801-7. [PMID: 8003051 DOI: 10.1002/art.1780370604] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
OBJECTIVE To determine if patients with fibromyalgia syndrome (FMS) are more susceptible to activity-induced muscle damage than are healthy subjects. METHODS Eleven FMS patients and 10 healthy subjects performed concentric and eccentric exercise with their dominant and nondominant forearms, respectively. 31P magnetic resonance spectroscopy (to assess inorganic phosphate [P(i)] and phosphocreatine [PCr]) and dolorimetry (to assess pain) were performed before and 20 minutes after exercise and at 4 subsequent 24-hour intervals. RESULTS Neither group exhibited increased P(i)/PCr ratios or reduced dolorimetry scores following the exercise protocols. FMS patients did display a phosphodiester resonance at a higher rate than healthy subjects (37% versus 12%), but this was not related to the exercise. CONCLUSION Unchanged P(i)/PCr ratios and dolorimetry scores following acute exercise provide evidence against the hypothesis that FMS patients are more susceptible to activity-induced muscle damage than are healthy subjects, although P(i)/Pcr and pain may not adequately document such damage. The frequent occurrence of phosphodiester in the spectra of FMS patients may indicate a sarcolemmal abnormality in these subjects.
Collapse
Affiliation(s)
- S A Jubrias
- Department of Radiology, University of Washington Medical Center, Seattle 98195
| | | | | |
Collapse
|
32
|
Abstract
It is well documented that repeated voluntary activity or electrical stimulation of skeletal muscle results in a decline in force production or power output. However, the precise physiological causes of "muscle fatigue" are not yet well understood. It is conceivable that the mechanism(s) may lie either in the conduction of action potentials in the central and peripheral nervous systems or in the transformation of the electrical event into mechanical force production by the muscle itself. In fact, none of the components of the electrical pathway from generation of impulses in the brain to their conduction over the neuron and the excitable membranes of the muscle can as yet be ruled out as potential contributors to the fatigue process. Relative to that on conduction failure, more information exists concerning the possibility that a defect in the excitation contraction coupling process in skeletal muscle, e.g., intracellular acidosis, inadequate supply of energy for contraction, or a disruption in Ca2+ homeostasis may also be significant in compromising force production following sustained activity. Despite this, the amount of conflicting data derived from these experiments has hindered the resolution of this question. In the future more attention must be given to such issues as the type of activity used to elicit fatigue and the fiber composition of the muscles studied. This is imperative as these factors clearly impact the nature of correlations between the biochemical and physiological events in muscle that are required to support prospective fatigue mechanisms.
Collapse
Affiliation(s)
- K A Luckin
- Department of Exercise and Movement Science, University of Oregon, Eugene 97403
| | | | | | | | | |
Collapse
|