scholarly journals 108 President Oral Presentation Pick: Select skeletal muscle mitochondrial measures in Thoroughbred weanlings are related to race earnings and sire

2020 ◽  
Vol 98 (Supplement_4) ◽  
pp. 85-85
Author(s):  
Chloey P Guy ◽  
Christine M Latham ◽  
Randi N Owen ◽  
Ashley L Fowler ◽  
Sarah H White-Springer
Keyword(s):  
Skeletal Muscle ◽  
Complex I ◽  
Fixed Effects ◽  
Linear Models ◽  
Citrate Synthase ◽  
Pearson Correlation ◽  
Gluteus Medius ◽  
Volume Density ◽  
Complex Ii ◽  
And Training

Abstract Quantifiable, cellular differences of individuals are not widely used in breeding and training decisions in the equine industry. Our objective was to determine if mitochondrial parameters in weanling Thoroughbreds were related to sire or lifetime race earnings. We hypothesized that weanling skeletal muscle mitochondrial capacity would be positively correlated with race earnings. Gluteus medius muscle samples were collected from racing-bred Thoroughbred weanlings (n = 139; mean ± SD; 6.0 ± 0.4 mo) from 40 different sires over 3 years at 5 different farms and evaluated for mitochondrial volume density (citrate synthase activity; CS) and function (cytochrome c oxidase activity) by colorimetry, and oxidative (P) and electron transport system (E) capacities by high resolution respirometry; two- and three-year-old race earnings were available for a subset of 13 horses. Data were analyzed using mixed linear models with sire, sex, year of collection, and farm as fixed effects. Correlations between lifetime race earnings and mitochondrial measures were determined using Pearson Correlation Statistics. A main effect of sire was observed for weanling intrinsic (relative to CS activity) P with complex I substrates (P = 0.04) and the contribution of mitochondrial leak to O2 consumption (FCRL; P = 0.04). A trend was observed for the effect of sire on intrinsic mitochondrial leak (P = 0.09). Race earnings were positively correlated with integrated (relative to mg protein) leak (r = 0.7684, P = 0.009) and FCRL (r = 0.7035; P = 0.02). A trend for a negative correlation between E with complex II substrates and race earnings was also observed (r = -0.4775, P = 0.09), No other measures were influenced by sire, nor were correlated with race earnings. Our previous work has indicated a preferential use of complex I in breeds bred for short-duration racing (Thoroughbreds) compared to distance racing breeds (Standardbreds) that relied more heavily on complex II. Mitochondrial measures in weanlings may be utilized to inform future breeding and training decisions in horses.

scholarly journals 107 Skeletal muscle mitochondrial parameters correlate with sales price in weanling racing-bred Thoroughbred horses

2020 ◽  
Vol 98 (Supplement_4) ◽  
pp. 86-86
Author(s):  
Chloey P Guy ◽  
Christine M Latham ◽  
Randi N Owen ◽  
Ashley L Fowler ◽  
Sarah H White-Springer
Keyword(s):  
Skeletal Muscle ◽  
Complex I ◽  
Citrate Synthase ◽  
Pearson Correlation ◽  
Coupling Efficiency ◽  
Gluteus Medius ◽  
Volume Density ◽  
Sales Price ◽  
Correlation Statistics ◽  
Race Performance

Abstract Thoroughbred horse sales prices rely heavily on animal conformation and ancestral race performance, as well as the current economic landscape. However, little information exists on the relationship between physiological parameters and sales price. We aimed to test the hypothesis that weanling sales price would positively correlate with skeletal muscle mitochondrial parameters in racing-bred Thoroughbreds. Gluteus medius muscle samples were collected from racing-bred Thoroughbred weanlings (n = 19; mean ± SD; 5.7 ± 0.3 mo) and evaluated for mitochondrial volume density (citrate synthase activity; CS) and function (cytochrome c oxidase activity; COX) by colorimetry, and oxidative and electron transport system capacities by high resolution respirometry. Horses were sold at the 2018 and 2019 Keeneland November Breeding Stock Sales at 8.5 ± 0.7 mo of age. Data were analyzed using Pearson Correlation Statistics in SAS (v9.4). Weanling sales price was positively correlated with intrinsic mitochondrial function (COX activity per unit CS; r = 0.6269, P = 0.004) and coupling efficiency with substrates for complex I+II (r = 0.4424, P = 0.05). A trend for a negative correlation was observed between weanling sales price and CS activity (r = -0.4179, P = 0.07), while a trend for a positive correlation between sales price and intrinsic oxidative phosphorylation capacity with complex I substrates (r = 0.3974, P = 0.09) was observed. In this cohort of weanling Thoroughbreds, mitochondrial parameters measured at 6 mo of age correlated with sales price at 8 mo of age. Implications of these relationships as they relate to race performance should be further investigated.

241 Skeletal Muscle Mitochondrial Capacities Are Impacted by Breed and Temperament in Young Angus and Brahman Steers

2021 ◽  
Vol 99 (Supplement_3) ◽  
pp. 127-127
Author(s):  
Chloey P Guy ◽  
Lauren T Wesolowski ◽  
Audrey L Earnhardt ◽  
Dustin Law ◽  
Don A Neuendorff ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Fixed Effects ◽  
Linear Models ◽  
Citrate Synthase ◽  
Volume Density ◽  
Skeletal Muscle Mitochondria ◽  
Mitochondrial Volume ◽  
Mitochondrial Volume Density ◽  
Brahman Steers ◽  
The Impact

Abstract Temperament impacts skeletal muscle mitochondria in Brahman heifers, but this has not been investigated in steers or between cattle breeds. We hypothesized mitochondrial measures would be greater in Angus than Brahman, temperamental than calm steers, and the trapezius (TRAP) than the longissimus thoracis (LT) muscle. Samples from calm (n = 13 per breed), intermediate (n = 12 per breed), and temperamental (n=13 per breed) Angus and Brahman steers (mean±SD 10.0±0.8 mo) were evaluated for mitochondrial enzyme activities via colorimetry. Calm and temperamental LT samples were evaluated for oxidative phosphorylation (P) and electron transfer (E) capacities by high-resolution respirometry. Data were analyzed using linear models with fixed effects of breed, muscle, temperament, and all interactions. Brahman tended to have greater mitochondrial volume density (citrate synthase activity; CS) than Angus (P = 0.08), while intrinsic (relative to CS) mitochondrial function (cytochrome c oxidase activity) was greater in Angus than Brahman (P = 0.001) and greater in TRAP than LT (P = 0.008). Angus exhibited greater integrative (per mg tissue) and intrinsic P with complex I (PCI), P with complexes I+II (PCI+II), maximum noncoupled E, and E with complex II (ECII; P ≤ 0.04) and tended to have greater intrinsic leak (P = 0.1) than Brahman. Contribution of PCI to total E was greater in Angus than Brahman (P = 0.01), while contribution of ECII to total E was greater in Brahman than Angus (P = 0.05). A trend for the interaction of breed and temperament (P = 0.07) indicated calm Angus had the greatest intrinsic ECII (P ≤ 0.03) while intrinsic ECII was similar between temperamental Angus and calm and temperamental Brahman. Integrative PCI+II and ECII, and the contribution of PCI and PCI+II to overall E tended to be greater in temperamental than calm steers (P ≤ 0.09), while intrinsic ECII tended to be greater in calm than temperamental steers (P = 0.07). The impact of these mitochondrial differences on meat quality measures remains to be determined.

507 Late-Breaking: Heat Stress and Mitoq Supplementation Impact Skeletal Muscle Mitochondrial Capacities in Pigs

2021 ◽  
Vol 99 (Supplement_3) ◽  
pp. 204-205
Author(s):  
Lauren T Wesolowski ◽  
Chloey P Guy ◽  
Edith J Mayorga ◽  
Tori E Rudolph ◽  
Alyssa D Freestone ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Heat Stress ◽  
Mitochondrial Function ◽  
Fixed Effects ◽  
Linear Models ◽  
Citrate Synthase ◽  
Volume Density ◽  
Semitendinosus Muscle ◽  
Mitochondrial Volume ◽  
Mitochondrial Volume Density

Abstract Heat stress can negatively impact pig health and performance but the effects of heat stress on skeletal muscle mitochondrial function are largely unknown. We hypothesized that mitochondrial function and capacity would be impaired in heat stressed (HS) compared to thermoneutral (TN) pigs but mitochondrially-targeted coenzyme Q (MitoQ) supplementation would rescue the impairment. Oxidative portions of the semitendinosus muscle were evaluated from TN and HS gilts receiving no supplementation (CON) or MitoQ for 2 d prior to and during the 24h environmental heat treatment (n = 8 per group). Mitochondrial oxidative phosphorylation (P) and electron transfer (E) capacities were determined via high resolution respirometry and mitochondrial volume density and function were quantified by citrate synthase (CS) and cytochrome c oxidase activities, respectively. Data were analyzed using linear models in SAS v9.4 with fixed effects of heat, MitoQ treatment (trt), and heat×trt interaction. There were trends for the interaction of trt and heat (P≤0.1) on integrative (per mg tissue) and intrinsic (relative to CS) P with complexes I and II (PCI+II), maximum noncoupled E (ECI+II), and E with complex II only (ECII), in which all measures were greater in HS-MitoQ than TN-MitoQ (P≤0.03), but measures did not differ due to HS in CON pigs. The contribution of leak to total E (flux control ratio, FCRLeak) was lesser in HS-MitoQ than HS-CON, TN-CON, and TN-MitoQ (P≤0.02). The FCRPCI was greater (P≤0.05) while the FCRPCI+II was lesser (P=0.01) in TN compared to HS pigs. Finally, the FCRPCI+II was greater (P=0.02) while the FCRECII tended to be lesser (P=0.09) for CON than MitoQ pigs. Neither mitochondrial volume density nor function were affected by HS or MitoQ supplementation. In total, these data indicate improved mitochondrial capacities following heat stress in pigs receiving MitoQ but no difference in mitochondrial capacities in unsupplemented, HS pigs.

scholarly journals Temperament influences mitochondrial capacity in skeletal muscle from 8 through 18 mo of age in Brahman heifers

2020 ◽  
Vol 98 (10) ◽  
Author(s):  
Randi N Owen ◽  
Christine M Latham ◽  
Charles R Long ◽  
Ronald D Randel ◽  
Thomas H Welsh ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Product Quality ◽  
Repeated Measures ◽  
Complex I ◽  
Citrate Synthase ◽  
Serum Cortisol ◽  
System Capacity ◽  
Complex Ii ◽  
Potential Link ◽  
Muscle Groups

Abstract Temperamental cattle tend to yield carcasses of poorer quality, and Brahman cattle are reportedly more temperamental than non-indicus cattle breeds. A potential link between temperament and product quality may be mitochondrial activity. We hypothesized that mitochondrial measures would be greater in temperamental compared with calm heifers and that the relationships between temperament and mitochondria would persist as heifers age. Serum cortisol and skeletal muscle (longissimus thoracis [LT] and trapezius [TRAP]) mitochondrial profiles and antioxidant activities were quantified from the same calm (n = 6) and temperamental (n = 6) Brahman heifers at 8, 12, and 18 mo of age. Data were analyzed using a mixed model ANOVA in SAS (9.4) with repeated measures. Serum cortisol was greater in temperamental compared with calm heifers throughout the study (P = 0.02). Mitochondrial volume density (citrate synthase [CS] activity) increased over time (P < 0.0001) but was similar between temperament and muscle groups. Mitochondrial function (cytochrome c oxidase activity) was greatest in the temperamental LT at 8 mo of age (P ≤ 0.0006), greatest in the temperamental TRAP at 18 mo of age (P ≤ 0.003), and did not differ by temperament at 12 mo of age. Integrative (relative to tissue wet weight) mitochondrial oxidative phosphorylation capacity with complex I substrates (PCI), PCI plus complex II substrate (PCI+II), noncoupled electron transfer system capacity (ECI+II), and E with functional complex II only (ECII) were greater in the TRAP than LT for calm heifers at all ages (P ≤ 0.002), but were similar between muscle groups in temperamental heifers. Overall, calm heifers tended to have greater intrinsic (relative to CS activity) PCI and flux control of PCI+II (P ≤ 0.1) than temperamental heifers, indicating greater utilization of complex I paired with greater coupling efficiency in calm heifers. Within the LT, integrative PCI+II was greater (P = 0.05) and ECI+II tended to be greater (P = 0.06) in temperamental compared with calm heifers. From 8- to 18-mo old, glutathione peroxidase (GPx) activity decreased (P < 0.0001) and superoxide dismutase activity increased (P = 0.02), and both were similar between muscle groups. The activity of GPx was greater in temperamental compared with calm heifers at 8 (P = 0.004) but not at 12 or 18 mo of age. These results detail divergent skeletal muscle mitochondrial characteristics of live Brahman heifers according to temperament, which should be further investigated as a potential link between temperament and product quality.

scholarly journals RAPID COMMUNICATION: Differential skeletal muscle mitochondrial characteristics of weanling racing-bred horses1

2019 ◽  
Vol 97 (8) ◽  
pp. 3193-3198 ◽  
Author(s):  
Christine M Latham ◽  
Clara K Fenger ◽  
Sarah H White
Keyword(s):  
Skeletal Muscle ◽  
Electron Transport ◽  
Transport System ◽  
Complex I ◽  
Management Practices ◽  
Citrate Synthase ◽  
Fiber Type ◽  
Gluteus Medius ◽  
Electron Transport System ◽  
Mitochondrial Density

Abstract Responses of equine skeletal muscle characteristics to growth and training have been shown to differ between breeds. These differential responses may arise in part because muscle fiber type and mitochondrial density differ between breeds, even in untrained racing-bred horses. However, it is not known when these breed-specific differences manifest. To test the hypothesis that weanling Standardbreds (SB) and Thoroughbreds (TB) would have higher mitochondrial measures than Quarter Horses (QH), gluteus medius samples were collected from SB (mean ± SD; 6.2 ± 1.0 mo; n = 10), TB (6.1 ± 0.5 mo; n = 12), and QH (7.4 ± 0.6 mo; n = 10). Citrate synthase (CS) and cytochrome c oxidase (CCO) activities were assessed as markers of mitochondrial density and function, respectively. Mitochondrial oxidative (P) and electron transport system (E) capacities were assessed by high-resolution respirometry (HRR). Data for CCO and HRR are expressed as integrated (per mg protein and per mg tissue wet weight, respectively) and intrinsic (per unit CS). Data were analyzed using PROC MIXED in SAS v 9.4 with breed as a fixed effect. Mitochondrial density (CS) was higher for SB and TB than QH (P ≤ 0.0007). Mitochondrial function (integrated and intrinsic CCO) was higher in TB and QH than SB (P ≤ 0.01). Integrated CCO was also higher in TB than QH (P < 0.0001). However, SB had higher integrated maximum P (PCI+II) and E (ECI+II) than QH (P ≤ 0.02) and greater integrated and intrinsic complex II-supported E (ECII) than both QH and TB (P ≤ 0.02), whereas TB exhibited higher integrated P with complex I substrates (PCI) than SB and QH (P ≤ 0.003) and higher integrated PCI+II and ECI+II than QH (P ≤ 0.02). In agreement, TB and QH had higher contribution of complex I (CI) to max E than SB (P ≤ 0.001), whereas SB had higher contribution of CII than QH and TB (P ≤ 0.002). Despite having higher mitochondrial density than QH and TB, SB showed lower CCO activity and differences in contribution of complexes to oxidative and electron transport system capacities. Breed differences in mitochondrial parameters are present early in life and should be considered when developing feeding, training, medication, and management practices.

scholarly journals Skeletal muscle mitochondrial function and exercise capacity are not impaired in mice with knockout of STAT3

2019 ◽  
Vol 127 (4) ◽  
pp. 1117-1127
Author(s):  
Jessica R. Dent ◽  
Byron Hetrick ◽  
Shahriar Tahvilian ◽  
Abha Sathe ◽  
Keenan Greyslak ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Electron Transport ◽  
Complex I ◽  
Physiological Function ◽  
Oxidative Capacity ◽  
Signal Transducer ◽  
Muscle Mitochondria ◽  
Complex Ii ◽  
Skeletal Muscle Mitochondria ◽  
Transcription 3

Signal transducer and activator of transcription 3 (STAT3) was recently found to be localized to mitochondria in a number of tissues and cell types, where it modulates oxidative phosphorylation via interactions with the electron transport proteins, complex I and complex II. Skeletal muscle is densely populated with mitochondria although whether STAT3 contributes to skeletal muscle oxidative capacity is unknown. In the present study, we sought to elucidate the contribution of STAT3 to mitochondrial and skeletal muscle function by studying mice with muscle-specific knockout of STAT3 (mKO). First, we developed a novel flow cytometry-based approach to confirm that STAT3 is present in skeletal muscle mitochondria. However, contrary to findings in other tissue types, complex I and complex II activity and maximal mitochondrial respiratory capacity in skeletal muscle were comparable between mKO mice and floxed/wild-type littermates. Moreover, there were no genotype differences in endurance exercise performance, skeletal muscle force-generating capacity, or the adaptive response of skeletal muscle to voluntary wheel running. Collectively, although we confirm the presence of STAT3 in skeletal muscle mitochondria, our data establish that STAT3 is dispensable for mitochondrial and physiological function in skeletal muscle. NEW & NOTEWORTHY Whether signal transducer and activator of transcription 3 (STAT3) can regulate the activity of complex I and II of the electron transport chain and mitochondrial oxidative capacity in skeletal muscle, as it can in other tissues, is unknown. By using a mouse model lacking STAT3 in muscle, we demonstrate that skeletal muscle mitochondrial and physiological function, both in vivo and ex vivo, is not impacted by the loss of STAT3.

Possible Pathogenic Mechanism of Propofol Infusion Syndrome Involves Coenzyme Q

2015 ◽  
Vol 122 (2) ◽  
pp. 343-352 ◽  
Author(s):  
Arnaud Vincent Vanlander ◽  
Juergen Guenther Okun ◽  
Annick de Jaeger ◽  
Joél Smet ◽  
Elien De Latter ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Respiratory Chain ◽  
Citrate Synthase ◽  
Tissue Concentration ◽  
Electron Flow ◽  
Coenzyme Q ◽  
Propofol Infusion Syndrome ◽  
Complex Ii ◽  
Main Site ◽  
Mitochondrial Fatty Acid

Abstract Background: Propofol is a short-acting intravenous anesthetic agent. In rare conditions, a life-threatening complication known as propofol infusion syndrome can occur. The pathophysiologic mechanism is still unknown. Some studies suggested that propofol acts as uncoupling agent, others suggested that it inhibits complex I or complex IV, or causes increased oxidation of cytochrome c and cytochrome aa3, or inhibits mitochondrial fatty acid metabolism. Although the exact site of interaction is not known, most hypotheses point to the direction of the mitochondria. Methods: Eight rats were ventilated and sedated with propofol up to 20 h. Sequential biopsy specimens were taken from liver and skeletal muscle and used for determination of respiratory chain activities and propofol concentration. Activities were also measured in skeletal muscle from a patient who died of propofol infusion syndrome. Results: In rats, authors detected a decrease in complex II+III activity starting at low tissue concentration of propofol (20 to 25 µM), further declining at higher concentrations. Before starting anesthesia, the complex II+III/citrate synthase activity ratio in liver was 0.46 (0.25) and in skeletal muscle 0.23 (0.05) (mean [SD]). After 20 h of anesthesia, the ratios declined to 0.17 (0.03) and 0.12 (0.02), respectively. When measured individually, the activities of complexes II and III remained normal. Skeletal muscle from one patient taken in the acute phase of propofol infusion syndrome also shows a selective decrease in complex II+III activity (z-score: −2.96). Conclusion: Propofol impedes the electron flow through the respiratory chain and coenzyme Q is the main site of interaction with propofol.

scholarly journals Adaptations in Mitochondrial Enzymatic Activity Occurs Independent of Genomic Dosage in Response to Aerobic Exercise Training and Deconditioning in Human Skeletal Muscle

Cells ◽  
2019 ◽  
Vol 8 (3) ◽  
pp. 237 ◽  
Author(s):  
Andreas Fritzen ◽  
Frank Thøgersen ◽  
Kasper Thybo ◽  
Christoffer Vissing ◽  
Thomas Krag ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Exercise Training ◽  
Enzymatic Activity ◽  
Endurance Exercise ◽  
Complex I ◽  
Citrate Synthase ◽  
Knee Extensor ◽  
Mitochondrial Complex ◽  
Membrane Markers ◽  
Endurance Exercise Training

Mitochondrial DNA (mtDNA) replication is thought to be an integral part of exercise-training-induced mitochondrial adaptations. Thus, mtDNA level is often used as an index of mitochondrial adaptations in training studies. We investigated the hypothesis that endurance exercise training-induced mitochondrial enzymatic changes are independent of genomic dosage by studying mtDNA content in skeletal muscle in response to six weeks of knee-extensor exercise training followed by four weeks of deconditioning in one leg, comparing results to the contralateral untrained leg, in 10 healthy, untrained male volunteers. Findings were compared to citrate synthase activity, mitochondrial complex activities, and content of mitochondrial membrane markers (porin and cardiolipin). One-legged knee-extensor exercise increased endurance performance by 120%, which was accompanied by increases in power output and peak oxygen uptake of 49% and 33%, respectively (p < 0.01). Citrate synthase and mitochondrial respiratory chain complex I–IV activities were increased by 51% and 46–61%, respectively, in the trained leg (p < 0.001). Despite a substantial training-induced increase in mitochondrial activity of TCA and ETC enzymes, there was no change in mtDNA and mitochondrial inner and outer membrane markers (i.e. cardiolipin and porin). Conversely, deconditioning reduced endurance capacity by 41%, muscle citrate synthase activity by 32%, and mitochondrial complex I–IV activities by 29–36% (p < 0.05), without any change in mtDNA and porin and cardiolipin content in the previously trained leg. The findings demonstrate that the adaptations in mitochondrial enzymatic activity after aerobic endurance exercise training and the opposite effects of deconditioning are independent of changes in the number of mitochondrial genomes, and likely relate to changes in the rate of transcription of mtDNA.

Effect of hyperthermia and acidosis on equine skeletal muscle mitochondrial oxygen consumption

2020 ◽  
pp. 1-10
Author(s):  
M.S. Davis ◽  
M.R. Fulton ◽  
A. Popken
Keyword(s):  
Skeletal Muscle ◽  
Oxygen Consumption ◽  
Oxidative Phosphorylation ◽  
Muscle Fatigue ◽  
Mitochondrial Function ◽  
Mitochondrial Respiration ◽  
Complex I ◽  
Mitochondrial Oxygen Consumption ◽  
Biochemical Basis ◽  
Complex Ii

The skeletal muscle of exercising horses develops pronounced hyperthermia and acidosis during strenuous or prolonged exercise, with very high tissue temperature and low pH associated with muscle fatigue or damage. The purpose of this study was to evaluate the individual effects of physiologically relevant hyperthermia and acidosis on equine skeletal muscle mitochondrial function, using ex vivo measurement of oxygen consumption to assess the function of different mitochondrial elements. Fresh triceps muscle biopsies from 6 healthy unfit Thoroughbred geldings were permeabilised to permit diffusion of small molecular weight substrates through the sarcolemma and analysed in a high resolution respirometer at 38, 40, 42, and 44 °C, and pH=7.1, 6.5, and 6.1. Oxygen consumption was measured under conditions of non-phosphorylating (leak) respiration and phosphorylating respiration through Complex I and Complex II. Data were analysed using a one-way repeated measures ANOVA and data are expressed as mean ± standard deviation. Leak respiration was ~3-fold higher at 44 °C compared to 38 °C regardless of electron source (Complex I: 22.88±3.05 vs 8.08±1.92 pmol O2/mg/s), P=0.002; Complex II: 79.14±23.72 vs 21.43±11.08 pmol O2/mg/s, P=0.022), resulting in a decrease in efficiency of oxidative phosphorylation. Acidosis had minimal effect on mitochondrial respiration at pH=6.5, but pH=6.1 resulted in a 50% decrease in mitochondrial oxygen consumption. These results suggest that skeletal muscle hyperthermia decreases the efficiency of oxidative phosphorylation through increased leak respiration, thus providing a specific biochemical basis for hyperthermia-induced muscle fatigue. The effect of myocellular acidosis on mitochondrial respiration was minimal under typical levels of acidosis, but atypically severe acidosis can lead to impairment of mitochondrial function.

scholarly journals Mitochondrial Function in Oxidative and Glycolytic Bovine Skeletal Muscle Postmortem

2019 ◽  
Vol 3 (2) ◽  
Author(s):  
P. Ramos ◽  
L. Bell ◽  
S. Wohlgemuth ◽  
T. Scheffler
Keyword(s):  
Cytochrome C ◽  
Oxidative Phosphorylation ◽  
Outer Membrane ◽  
Functional Properties ◽  
Mitochondrial Function ◽  
Complex I ◽  
Fixed Effects ◽  
Citrate Synthase ◽  
Electron Flow ◽  
Coupling Efficiency

ObjectivesMitochondrial function in postmortem muscle is affected by decreasing oxygenation. Functional properties relating to energy production and integrity of mitochondria may influence development of meat quality characteristics. Therefore, the objective was to evaluate changes in mitochondrial function in oxidative and glycolytic muscles during the first 24h postmortem.Materials and MethodsSteers (n = 6) of primarily Angus (80 to 100%) genetics were harvested at approximately 18.5 mo and 630 kg live weight. Samples from the longissimus lumborum (LL) and diaphragm (Dia) were collected at 1, 3, and 24h postmortem. Fresh-preserved muscle samples were permeabilized using saponin, and muscle bundles (2–4 mg) were transferred to a high-resolution oxygraph for respiration measurements (oxygen consumption rate, OCR, pmol/sec/mg of tissue). Samples were assessed in duplicate under hyperoxia. First, pyruvate and malate were added to support the TCA cycle and assess leak respiration. Then, ADP was added to support electron flow through complex I. The influence of glutamate on NADH production (complex I) was tested, followed by complex II activation by succinate. Integrity of the mitochondria outer membrane was tested with cytochrome c. Next, an uncoupler (FCCP) was added to force the electron transport system (ETS) to maximum capacity. Citrate synthase (CS) activity (nmol/min/mg tissue) was determined in frozen samples and used as a marker of mitochondria content. Subsequently, respiration data were normalized to CS activity (pmol/sec/U CS) to account for differences in mitochondria content. Coupling efficiency of oxidative phosphorylation was calculated as 1– (Leak/ADP-stimulated oxidative phosphorylation capacity). Raw and normalized OCR were analyzed in a randomized block design, with slaughter date as block and fixed effects of muscle, time, and the interaction. Time was considered a repeated measure.ResultsMuscle type affected (P = 0.0002) leak OCR, with Dia showing a higher rate than LL. After ADP was added, mitochondria from Dia exhibited higher OCR at all times tested and at all steps, with OCR being 4 times higher after FCCP addition. Mitochondrial content, evidenced by greater (P < 0.0001) CS activity in Dia, largely explained differences in OCR between muscles. After OCR was normalized to CS activity, the 1 and 3h postmortem OCR from Dia and LL were similar (P > 0.05). However, at 24h postmortem, OCR after ADP, glutamate, and FCCP additions were greater (P < 0.05) in Dia mitochondria. Time, but not muscle, affected cytochrome c response. At 1h postmortem, cytochrome c increased OCR by 6.6%, supporting that mitochondria outer membrane integrity is not compromised. However, cytochrome c response at 3h postmortem increased 52.4%, indicating outer membrane damage. Coupling efficiency is different between muscles (P = 0.005) with Dia exhibiting greater efficiency.ConclusionDespite inherent metabolic differences between the LL and Dia, mitochondria from both muscles are intact and coupled at 1h postmortem. However, by 24h postmortem, functional properties of LL mitochondria are reduced compared to Dia. Declining mitochondrial function may be associated with calcium overload, mitochondrial fragmentation, and protease activation.

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