A low-cost 2-D sarcomere model to demonstrate titin-related mechanisms for force production.

Given the recently proposed three-filament theory of muscle contraction, we present a low-cost physical sarcomere model aimed at illustrating the role of titin in the production of active force in skeletal muscle. With inexpensive materials, it is possible to illustrate actin-myosin cross-bridge interactions between the thick and thin filaments and demonstrate the two different mechanisms by which titin is thought to contribute to active and passive muscle force. Specifically, the model illustrates how titin, a molecule with springlike properties, may increase its stiffness by binding free calcium upon muscle activation and reducing its extensible length by attaching itself to actin, resulting in the greater force-generating capacity after an active than a passive elongation that has been observed experimentally. The model is simple to build and manipulate, and demonstration to high school students was shown to result in positive perception and improved understanding of the otherwise complex titin-related mechanisms of force production in skeletal and cardiac muscles.NEW & NOTEWORTHY Our physical sarcomere model illustrates not only the classic view of muscle contraction, the sliding filament and cross-bridge theories, but also the newly discovered role of titin in force regulation, called the three-filament theory. The model allows for easy visualization of the role of titin in muscle contraction and aids in explaining complex muscle properties that are not captured by the traditional cross-bridge theory.

MDM2 Regulation of HIF Signaling Causes Microvascular Dysfunction in Hypertrophic Cardiomyopathy.

BACKGROUND: Microvasculature dysfunction is a common finding in pathologic remodeling of the heart and is thought to play an important role in the pathogenesis of hypertrophic cardiomyopathy (HCM), a disease caused by sarcomere gene mutations. We hypothesized that microvascular dysfunction in HCM was secondary to abnormal microvascular growth and could occur independent of ventricular hypertrophy. METHODS: We used multimodality imaging methods to track the temporality of microvascular dysfunction in HCM mouse models harboring mutations in the sarcomere genes Mybpc3 (cardiac myosin binding protein C3) or Myh6 (myosin heavy chain 6). We performed complementary molecular methods to assess protein quantity, interactions, and post-translational modifications to identify mechanisms regulating this response. We manipulated select molecular pathways in vivo using both genetic and pharmacological methods to validate these mechanisms. RESULTS: We found that microvascular dysfunction in our HCM models occurred secondary to reduced myocardial capillary growth during the early postnatal time period and could occur before the onset of myocardial hypertrophy. We discovered that the E3 ubiquitin protein ligase MDM2 (murine double minute 2) dynamically regulates the protein stability of both HIF1α (hypoxia-inducible factor 1 alpha) and HIF2α (hypoxia-inducible factor 2 alpha)/EPAS1 (endothelial PAS domain protein 1) through canonical and noncanonical mechanisms. The resulting HIF imbalance leads to reduced proangiogenic gene expression during a key period of myocardial capillary growth. Reducing MDM2 protein levels by genetic or pharmacological methods normalized HIF protein levels and prevented the development of microvascular dysfunction in both HCM models. CONCLUSIONS: Our results show that sarcomere mutations induce cardiomyocyte MDM2 signaling during the earliest stages of disease, and this leads to long-term changes in the myocardial microenvironment.

emperature, pH and sarcomere length of Caiman yacare in different body weight categories at slaughter / Temperatura, pH e comprimento de sarcômero de Caiman yacare em diferentes categorias de peso corporal ao abate

The objective of this work was to characterize the internal temperature of the carcass, pH and sarcomere length in four categories of body weight at a slaughter. The categories were: category 1, animals up to 1.5 kg, category 2, animals from 1.501 to 2.5 kg, category 3, animals from 2.501 to 3.5 kg and category 4, animals over 3.501 kg. The time intervals evaluated were 0.5, 2, 4, 6, 8, 10, 12, 14, 16, 18, 24 and 36 hours after bleeding, therefore, a factorial scheme (4 x 12) was used, in which where four categories of pre-slaughter weight and the behavior of the carcasses during the post-slaughter time were evaluated. There was no interaction effect between the weight categories and the time for the variation of the carcass internal temperature, pH and sarcomere length, but when only the time of rigor was evaluated, there were significant differences for the analyzed parameters. The internal temperature of the initial average carcass (0.5 hours) was 16.02°C, reaching 3.80°C at 36 hours post-slaughter. In addition, the lowest average pH found was at 24 hours, with a value of 5.39. Regarding the sarcomere length, the smallest mean length observed was 1.41 µm at 16 hours post-slaughter and the final mean length (36 hours) was 1.89 µm. It was concluded that the analyzed margin of the categories of body weight at slaughter did not interfere in the variation of temperature, pH and sarcomere length during the post-mortem of the Pantanal caiman.(AU)

O objetivo do trabalho foi caracterizar a temperatura interna da carcaça, o pH e o comprimento de sarcômero em quatro categorias de peso corporal ao abate. As categorias foram: categoria 1, animais com até 1,5 kg, categoria 2, animais de 1,501 a 2,5 kg, categoria 3, animais de 2,501 a 3,5 kg e categoria 4, animais acima de 3,501 kg. Os intervalos de tempo avaliados foram 0,5, 2, 4, 6, 8, 10, 12, 14, 16, 18, 24 e 36 horas, após a sangria, portanto, foi utilizado um esquema fatorial (4 x 12) que avaliou quatro categorias de peso e o comportamento das carcaças ao decorrer do tempo. Não houve efeito de interação entre as categorias de peso e o tempo para a variação da temperatura interna da carcaça, pH e comprimento de sarcômero, mas quando avaliado apenas o tempo de rigor, houve diferenças significativas para os parâmetros analisados. A temperatura interna da carcaça média inicial (0,5 horas) foi de 16,02°C, chegando a 3,80°C nas 36 horas pós-abate. Além disso, o menor pH médio encontrado foi as 24 horas, com valor de 5,39. Em relação ao comprimento de sarcômero o menor comprimento médio observado foi de 1,41 µm nas 16 horas pós-abate e o comprimento médio final (36 horas) foi de 1,89 µm. Conclui-se que a margem analisada das categorias de peso corporal ao abate, não interferiram na variação de temperatura, pH e comprimento de sarcômero durante o post mortem do jacaré-do-Pantanal.(AU)

Ultrastructural and Molecular Development of the Myotendinous Junction Triggered by Stretching Prior to Resistance Exercise.

The myotendinous junction (MTJ) is a highly specialized region of the locomotor apparatus. Here, we investigated the ultrastructural and molecular effects in the MTJ region after static stretching prior to the ladder-based resistance training. Thirty-two male, 60-day old Wistar rats were divided into four groups: Sedentary, Resistance Training, Stretching, and Stretching-Resistance Training. The gastrocnemius muscle was processed for transmission electron microscopy techniques and Western blot assay. We observed that the static stretching prior to the ladder-based resistance training increased the MTJ components, the fibroblast growth factor (FGF)-2 and FGF-6 protein expression. Also, we demonstrated the lower transforming growth factor expression and no difference in the lysyl oxidase expression after combined training. The MTJ alterations in response to combined training demonstrate adaptive mechanisms which can be used for the prescription or development of methods to reduce or prevent injuries in humans and promote the myotendinous interface benefit.

Beef of Nellore cattle has limited tenderization despite pH decline in Longissimus lumborum

Bos taurus indicus temperament is variable and affects beef tenderization. Our objective was to investigate temperament and performance of non­castrated Nellore and identify groups based on Longissimus lumborum (LL) pH decline as well as beef characteristics produced by those groups. We investigated 94 animals with a subset of carcasses (n = 24) selected based on LL pH at 24 h postmortem (pm) to represent two groups: resistant to pH decline (> 5.8 called pH­Res; n = 10) and normal (< 5.7 called pH­Nor; n = 14). Steaks were fabricated from the LL muscle and randomly assigned to aging (2, 7, 14, and 21 days). Sarcomere length, cooking loss, myofibrillar fragmentation index (MFI), and Warner­Bratzler shear force (WBSF) were determined. Data on temperament were investigated in a multivariate approach, while beef data were compared between groups using the analysis of variance. Rectal temperature at the beginning of the finishing phase and total weight gain were greater and related to animals in the pH­Res group (p < 0.01 and p = 0.03, respectively). Temperature and pH decline curves, sarcomere length, and cooking loss revealed that pH­Res produced beef with lower quality compared to the pH­Nor group. Results for MFI and WBSF did not show differences between groups within each time pm; however, overall steaks from pH­Res were tougher (p = 0.06). Incidence of LL pH between 5.8 and 5.9 at 24 h pm did not compromise the tenderization rate or extension; however, it affected the water holding capacity in this population of Nellore cattle.(AU)

Biomechanical Properties of the Sarcolemma and Costameres of Skeletal Muscle Lacking Desmin.

Intermediate filaments (IFs), composed primarily by desmin and keratins, link the myofibrils to each other, to intracellular organelles, and to the sarcolemma. There they may play an important role in transfer of contractile force from the Z-disks and M-lines of neighboring myofibrils to costameres at the membrane, across the membrane to the extracellular matrix, and ultimately to the tendon ("lateral force transmission"). We measured the elasticity of the sarcolemma and the connections it makes at costameres with the underlying contractile apparatus of individual fast twitch muscle fibers of desmin-null mice. By positioning a suction pipet to the surface of the sarcolemma and applying increasing pressure, we determined the pressure at which the sarcolemma separated from nearby sarcomeres, Pseparation, and the pressure at which the isolated sarcolemma burst, Pbursting. We also examined the time required for the intact sarcolemma-costamere-sarcomere complex to reach equilibrium at lower pressures. All measurements showed the desmin-null fibers to have slower equilibrium times and lower Pseparation and Pbursting than controls, suggesting that the sarcolemma and its costameric links to nearby contractile structures were weaker in the absence of desmin. Comparisons to earlier values determined for muscles lacking dystrophin or synemin suggest that the desmin-null phenotype is more stable than the former and less stable than the latter. Our results are consistent with the moderate myopathy seen in desmin-null muscles and support the idea that desmin contributes significantly to sarcolemmal stability and lateral force transmission.

Morphological Changes in the Myotendinous Junction of mdx Mice.

The myotendinous junction (MTJ) is the interface between muscle and tendon, and it is the main area of force transmission of the locomotor apparatus. Dystrophic processes promote pathological injury which affects the skeletal muscle and can influence the morphology of the MTJ. This study aimed to investigate the adaptations in MTJ morphology of mdx mice in the tibialis anterior muscle. Male mice (n = 24) were divided into Control­C57bl/10 and mdx­C57bl/10mdx (Duchenne muscular dystrophy experimental model). In the mdx group, centralized nuclei with a large area and greater deposition of type III collagen (fibrosis) were observed. Also, shorter sarcomeres and sarcoplasmatic projections of MTJ were observed. We concluded that the adaptations in mdx mice demonstrated extensive impairment in the MTJ region with reduced ultrastructures.

Numerical Simulation of a Physiological Mathematical Model of Energy Consumption in a Sarcomere / Simulación Numérica de un Modelo Matemático Fisiológico de Consumo de Energía en un Sarcómero

ABSTRACT The paradigm of biological systems provides a framework to quantify the behavior of biological processes. Mathematical modeling is one of the analytical tools of biological systems used to reproduce the variables of a system for prediction. This article presents the analysis of muscular contraction, the physiological process responsible of generating force in skeletal muscle, from the point of view of mathematical modeling. The aim is to provide numerical evidences about the force generated by the sarcomere, and the energy required to produce such a force. The proposed scheme includes a model to activate the contractile cycle, based on the action potential that reaches the neuromuscular junction, the calcium release into the sarcoplasm, the contraction response, and the quantification of the energy that the sarcomere requires to perform mechanical work. The results shows that the proposed scheme is acceptable because it reproduces experimental data of force, velocity, and energy reported in the literature. The results of the proposed scheme are encouraging to scale the model at the muscle or muscle group level, in such a way that the quantification of energy can be an alternative to the indirect estimation methods of energy consumption that currently exist.

Aquatic Training after Joint Immobilization in Rats Promotes Adaptations in Myotendinous Junctions.

The myotendinous junction (MTJ) is the muscle-tendon interface and constitutes an integrated mechanical unit to force transmission. Joint immobilization promotes muscle atrophy via disuse, while physical exercise can be used as an adaptative stimulus. In this study, we aimed to investigate the components of the MTJ and their adaptations and the associated elements triggered with aquatic training after joint immobilization. Forty-four male Wistar rats were divided into sedentary (SD), aquatic training (AT), immobilization (IM), and immobilization/aquatic training (IMAT) groups. The samples were processed to measure fiber area, nuclear fractal dimension, MTJ nuclear density, identification of telocytes, sarcomeres, and MTJ perimeter length. In the AT group, the maintenance of ultrastructure and elements in the MTJ region were observed; the IM group presented muscle atrophy effects with reduced MTJ perimeter; the IMAT group demonstrated that aquatic training after joint immobilization promotes benefits in the muscle fiber area and fractal dimension, in the MTJ region shows longer sarcomeres and MTJ perimeter. We identified the presence of telocytes in the MTJ region in all experimental groups. We concluded that aquatic training is an effective rehabilitation method after joint immobilization due to reduced muscle atrophy and regeneration effects on MTJ in rats.

Myotendinous Junction Components of Different Skeletal Muscles Present Morphological Changes in Obese Rats.

Obesity is characterized by excess adipose tissue and chronic inflammation and promotes extensive changes that can compromise skeletal muscles' structural and functional integrity. Obesity can seriously impact the force transmission region between the muscle and the tendon, the myotendinous junction (MTJ). The present study aimed to investigate the plasticity of muscle fibers and MTJ regions in high-fat diet-induced obesity in rat tibialis anterior (TA) and soleus (SO) muscles. Wistar rats were divided into control and obese groups (induced by a high-fat diet). The samples of TA and SO muscles were prepared for histochemical and ultrastructural analysis (sarcomeres and MTJ projection). In the muscle fiber, similar adaptations were observed between the muscles of the smaller fiber (types I and IIa) in the obesity results. The MTJ region demonstrated different adaptations between the analyzed muscles. The TA­MTJ region has shorter ultrastructures, while in the SO­MTJ region, the ultrastructures were larger. We conclude that obesity induced by a high-fat diet promotes similar adaptation in the muscle fibers; however, in the MTJ region, the sarcoplasmatic projections and adjacent sarcomere demonstrate different adaptations according to distinct muscle phenotypes.

Repercussions on sarcomeres of the myotendinous junction and the myofibrillar type adaptations in response to different trainings on vertical ladder.

The myofibrillary types establish to the skeletal muscle functional and adaptive properties that influence the sarcomeric arrangement during muscle contraction and may have repercussions on an important related force transmission region of the locomotor apparatus, the myotendinous junction (MTJ). This study aimed to describe changes in myofibrillary type and sarcomeric lengths in the belly muscle and MTJ of the soleus and plantaris muscles associated with training protocols in vertical ladder. Thirty adults male Wistar rats were divided into three groups (n = 10): Control (CTR), No-load Training (NLT), and Load Training (LT). Morphoquantitative analysis of different fibers types and sarcomere lengths were performed in distinct regions of plantaris and soleus muscles. In the plantaris muscle with both trainings, there was an increase in the cross-sectional area (CSA) in Type I and II fibers (p < .0001) while sarcomeric lengths revealed greater lengths in the proximal and distal sarcomeres of NLT, although in the LT we found greater lengths in the belly and MTJ sarcomeres. The soleus muscle showed an increase in CSA muscle fiber only in the NLT (p < .0001) and revealed alterations in belly and MTJ sarcomere lengths with training. We concluded that plantaris muscle has an adaptive effect directly associated with training load, with hypertrophy in both trainings and sarcomere length inverse from belly and MTJ, in LT associated with increased force generation and transmission at the MTJ, although soleus muscle has a lower adaptive response to training stimuli with variation in the belly and distal sarcomere of the MTJ.

Beef quality of Nellore steers fed dried or rehydrated and ensiled corn or sorghum grains / Calidad de la carne de Ganado Nelore alimentado con grano de maíz o sorgo seco o rehidratado y ensilado / Qualidade de carne de bovinos Nelore alimentados com grãos de milho ou sorgo seco ou reidratado e ensilado

Abstract Background: Rehydration of grains, such as corn and sorghum, is used to increase nutrient absorption. However, the effect of this practice on meat quality is poorly understood. Objective: To evaluate the effects of type of grain and processing on the meat quality of Nellore steers in a feedlot. Methods: Twenty-four non-castrated Nellore steers (270 ± 53 kg initial body weight) were distributed in a completely randomized 2×2 factorial design, with six replicates. The first factor was cereal type (corn or sorghum), and the second was the grain processing (dry or rehydrated and ensiled). The diets were composed of 30% corn silage and 70% concentrate. Sixty days before the beginning of the experiment, corn and sorghum grains were rehydrated and ensiled. The animals were slaughtered after 140 days of confinement. Meat quality analyses were determined in samples of fresh and aged meat (7 days) from the Longissimus lumborum muscle. Results: no difference between treatments was observed for carcass pH and L* (lightness), a* (redness), and b* (yellowness) values, shear force, thawing and cooking losses, and chemical composition of meat (p>0.05). The b* (yellowness) value of subcutaneous fat was higher in steers fed corn, regardless of grain processing (p=0.03). Sarcomere length was higher in aged meat of steers fed sorghum, regardless of processing method (p=0.01). Conclusions: the grain processing method does not affect beef quality; however, grain type can affect subcutaneous fat color and sarcomere length of aged beef.

Resumen Antecedentes: La rehidratación de granos, tales como maíz y sorgo, se usa para aprovechar mejor sus nutrientes. Sin embargo, es poco conocido el efecto de esta práctica sobre la calidad de la carne. Objetivo: Evaluar los efectos del tipo de cereal y su procesamiento sobre la calidad de carne de toretes Nelore en confinamiento. Métodos: Veinticuatro novillos Nelore enteros con un peso promedio inicial de 270 ± 53 kg, se distribuyeron en un diseño factorial 2×2 completamente aleatorizado (n=6). El primer factor fue el tipo de cereal (maíz o sorgo) y el segundo fue su procesamiento (seco o rehidratado y ensilado). Las dietas estuvieron compuestas por 28,44% de ensilaje de maíz y 71,56% de concentrado. Sesenta días antes de iniciar el experimento, los granos de maíz y sorgo se rehidrataron y ensilaron. Los animales se sacrificaron después de 140 días de confinamiento. La calidad de la carne se determinó en muestras de carne fresca y madurada (7 días) obtenidas del músculo Longissimus lumborum. Resultados: No hubo diferencias entre tratamientos para el pH de las canales, ni para los valores de color (L* "luminosidad", a* "intensidad de rojo" y b* "intensidad de amarillo"), fuerza de corte, composición química, o pérdidas de agua por descongelamiento o cocción (p>0,05). El valor de b* de la grasa subcutánea fue mayor en los novillos alimentados con maíz, independientemente del tipo de procesamiento (p=0,03). La longitud de sarcómero fue más alto en la carne madurada de novillos alimentados con sorgo, sin importar el método de procesamiento (p=0,01). Conclusiones: El método de procesamiento del grano no afecta la calidad de la carne; sin embargo, el tipo de cereal afecta el color de la grasa subcutánea y la longitud del sarcómero de la carne madurada.

Resumo Antecedentes: A reidratação de grãos, como milho e sorgo, tem sido usada para aumentar a utilização de seus nutrientes. Contudo, o efeito dessa prática na qualidade da carne é pouco compreendido. Objetivo: Avaliar os efeitos do tipo de grão de cereais e seu processamento sobre a qualidade da carne de bovinos confinados. Métodos: Vinte e quatro bovinos Nelore não castrados, com peso corporal médio inicial de 270 ± 53 kg foram distribuídos em delineamento inteiramente casualizado, fatorial 2×2, com seis repetições. O primeiro fator foi o tipo de grão de cereal no concentrado (milho ou sorgo), e o segundo foi o processamento destes grãos (seco ou reidratado e ensilado). As dietas foram compostas por 28,44% de silagem de milho e 71,56% de concentrado. Sessenta dias antes do início do experimento, os grãos de milho e sorgo foram reidratados e ensilados. Os animais foram abatidos após 140 dias de confinamento. As análises de qualidade da carne foram determinadas em amostras não maturadas e maturadas (7 dias) obtidas do músculo Longissimus lumborum. Resultados: Não houve diferenças significativas (p>0,05) entre os tratamentos para pH da carcaça e L* (luminosidade), a* (intensidade de vermelho), b* (intensidade de amarelo), força de cisalhamento, perdas por descongelamento, perdas por cocção, perdas totais e composição química da carne. O valor de b* da gordura subcutânea foi maior (p=0,03) em bovinos alimentados com dietas contendo grãos de milho, independentemente do tipo de processamento. O comprimento de sarcômero foi maior na carne maturada de novilhos alimentados com sorgo, independente do método de processamento (p=0,01). Conclusões: O método de processamento dos grãos não afetou a qualidade da carne bovina, no entanto, a cor da gordura subcutânea e o comprimento de sarcômero da carne maturada foram afetados pelo tipo de grão.

MEF2C repressor variant deregulation leads to cell cycle re-entry and development of heart failure.

BACKGROUND: A pathophysiological link exists between dysregulation of MEF2C transcription factors and heart failure (HF), but the underlying mechanisms remain elusive. Alternative splicing of MEF2C exons α, ß and γ provides transcript diversity with gene activation or repression functionalities. METHODS: Neonatal and adult rat ventricular myocytes were used to overexpress MEF2C splicing variants γ+ (repressor) or γ-, or the inactive MEF2Cγ+23/24 (K23T/R24L). Phenotypic alterations in cardiomyocytes were determined by confocal and electron microscopy, flow cytometry and DNA microarray. We used transgenic mice with cardiac-specific overexpression of MEF2Cγ+ or MEF2Cγ- to explore the impact of MEF2C variants in cardiac phenotype. Samples of non-infarcted areas of the left ventricle from patients and mouse model of myocardial infarction were used to detect the expression of MEF2Cγ+ in failing hearts. FINDINGS: We demonstrate a previously unrealized upregulation of the transrepressor MEF2Cγ+ isoform in human and mouse failing hearts. We show that adenovirus-mediated overexpression of MEF2Cγ+ downregulates multiple MEF2-target genes, and drives incomplete cell-cycle reentry, partial dedifferentiation and apoptosis in the neonatal and adult rat. None of these changes was observed in cardiomyocytes overexpressing MEF2Cγ-. Transgenic mice overexpressing MEF2Cγ+, but not the MEF2Cγ-, developed dilated cardiomyopathy, correlated to cell-cycle reentry and apoptosis of cardiomyocytes. INTERPRETATION: Our results provide a mechanistic link between MEF2Cγ+ and deleterious abnormalities in cardiomyocytes, supporting the notion that splicing dysregulation in MEF2C towards the selection of the MEF2Cγ+ variant contributes to the pathogenesis of HF by promoting cardiomyocyte dropout. FUNDING: São Paulo Research Foundation (FAPESP); Brazilian National Research Council (CNPq).

Toughness in Santa Inês lamb meat has negative impact on consumer evaluation / Dureza na carne de cordeiros Santa Inês tem impacto negativo na avaliação do consumidor

Meat tenderness is a major attribute for consumers worldwide. However, few studies investigate the importance of lamb meat tenderness for Brazilian consumers. This study assessed consumers evaluation of lamb meat with high shear forces. Eight lambs were slaughtered at 32.5±2.5kg of live weight and 5 to 6 months of age. The Longissimus dorsi muscle from both half carcasses was randomly assigned to four different postmortem processes: Tough Meat (TM), obtained by cold shortening, Fresh Meat (FM), Aging for 3 (A3) and 7 (A7) days postmortem . The variables measured were the sarcomere length, shear force (WBSF) and myofibrillar fragmentation index. We also applied the sensory analysis using affective acceptance tests with hedonic scale of nine points to measure texture, juiciness and overall quality of the meat. The postmortem processing for TM resulted in shorter sarcomere and greater shear values (p <0.05) compared to all other samples, while FM, A3 and A7, did not differ between the samples. Myofibrillar fragmentation was greater for A7 compared to TM (p <0.05), while FM and A3 showed intermediate values that did not differ between the treatments. In the sensory analysis, TM samples received significantly lower scores (p <0.01) for all attributes compared to other treatments and the attributes were not different between the post rigor processes. Consumers identified and evaluated negatively the meat samples with high WBSF. However, further studies are needed to elucidate the impact of smaller differences in WBSF, at intermediate values, on consumers evaluation.(AU)

A maciez da carne é um atributo importante para os consumidores do mundo todo. Porém, ainda faltam estudos sobre sua importância na área de carne de cordeiro para consumidores brasileiros. O objetivo do estudo foi verificar a avaliação dos consumidores em relação à carne de cordeiro com força de cisalhamento elevada. Oito cordeiros foram abatidos com 32,5 ± 2,5kg de peso vivo e 5 a 6 meses de idade. O músculo Longissimus dorsi das meias carcaças foi distribuído aleatoriamente em quatro diferentes processamentos postmortem: Carne Endurecida (CE), obtido pelo encurtamento pelo frio, Carne Fresca (CF), maturada por 3 (M3) e 7 (M7) dias postmortem . As variáveis ​​medidas foram comprimento do sarcômero, força de cisalhamento (FC), índice de fragmentação miofibrilar (IFM)e testes sensoriais de aceitação afetiva com escala hedônica de nove pontos para textura, suculência e qualidade global. O processamento postmortem para CE resultou em menor sarcômero e maiores valores de FC (p <0,05) em comparação com outras amostras, enquanto estas não diferiram entre si. O IFM foi maior para M7 em relação à CE (p <0,05), enquanto CF e M3 apresentaram valores intermediários que não diferiram. Noteste sensorial, as amostras de CE receberam escores menores (p <0,01) para todos os atributos comparados aos demais tratamentos, que não diferiram entre si. Os consumidores avaliaram negativamente a carne que apresentou alta FC. Porém, estudos devem ser realizados para elucidar o impacto de diferenças menores, em faixas intermediárias de FC, na avaliação do consumidor.(AU)

Toughness in Santa Inês lamb meat has negative impact on consumer evaluation / Dureza na carne de cordeiros Santa Inês tem impacto negativo na avaliação do consumidor

Meat tenderness is a major attribute for consumers worldwide. However, few studies investigate the importance of lamb meat tenderness for Brazilian consumers. This study assessed consumers’ evaluation of lamb meat with high shear forces. Eight lambs were slaughtered at 32.5±2.5kg of live weight and 5 to 6 months of age. The Longissimus dorsi muscle from both half carcasses was randomly assigned to four different postmortem processes: Tough Meat (TM), obtained by cold shortening, Fresh Meat (FM), Aging for 3 (A3) and 7 (A7) days postmortem . The variables measured were the sarcomere length, shear force (WBSF) and myofibrillar fragmentation index. We also applied the sensory analysis using affective acceptance tests with hedonic scale of nine points to measure texture, juiciness and overall quality of the meat. The postmortem processing for TM resulted in shorter sarcomere and greater shear values (p <0.05) compared to all other samples, while FM, A3 and A7, did not differ between the samples. Myofibrillar fragmentation was greater for A7 compared to TM (p <0.05), while FM and A3 showed intermediate values that did not differ between the treatments. In the sensory analysis, TM samples received significantly lower scores (p <0.01) for all attributes compared to other treatments and the attributes were not different between the post rigor processes. Consumers identified and evaluated negatively the meat samples with high WBSF. However, further studies are needed to elucidate the impact of smaller differences in WBSF, at intermediate values, on consumers’ evaluation.

A maciez da carne é um atributo importante para os consumidores do mundo todo. Porém, ainda faltam estudos sobre sua importância na área de carne de cordeiro para consumidores brasileiros. O objetivo do estudo foi verificar a avaliação dos consumidores em relação à carne de cordeiro com força de cisalhamento elevada. Oito cordeiros foram abatidos com 32,5 ± 2,5kg de peso vivo e 5 a 6 meses de idade. O músculo Longissimus dorsi das meias carcaças foi distribuído aleatoriamente em quatro diferentes processamentos postmortem: Carne Endurecida (CE), obtido pelo encurtamento pelo frio, Carne Fresca (CF), maturada por 3 (M3) e 7 (M7) dias postmortem . As variáveis ​​medidas foram comprimento do sarcômero, força de cisalhamento (FC), índice de fragmentação miofibrilar (IFM)e testes sensoriais de aceitação afetiva com escala hedônica de nove pontos para textura, suculência e qualidade global. O processamento postmortem para CE resultou em menor sarcômero e maiores valores de FC (p <0,05) em comparação com outras amostras, enquanto estas não diferiram entre si. O IFM foi maior para M7 em relação à CE (p <0,05), enquanto CF e M3 apresentaram valores intermediários que não diferiram. Noteste sensorial, as amostras de CE receberam escores menores (p <0,01) para todos os atributos comparados aos demais tratamentos, que não diferiram entre si. Os consumidores avaliaram negativamente a carne que apresentou alta FC. Porém, estudos devem ser realizados para elucidar o impacto de diferenças menores, em faixas intermediárias de FC, na avaliação do consumidor.

Qualitative characteristics of the Longissimus thoracic lumborum muscle of Nellore cattle during different maturation periods / Características qualitativas do Longissimus thoracic lumborum de bovinos Nelore maturado por diferentes períodos

The effect of maturation on the physical (pH, color, weight loss on cooking, and shear force) and biological (microbiology, concerning mesophiles and psychrotrophiles, and sarcomere length) characteristics of the Longissimus thoracic lumborum muscle of adult Nellore cattle was assessed over four maturation periods (0, 7, 14, and 21 days) and two cut thicknesses (2.5 and 7.5 cm). Sixty-four Longissimus thoracic lumborum muscles from castrated Nellore males were purchased from Frigorífico Nutrial, Sergipe, Brazil. The study was performed using a completely randomized design, corresponding to a 2 x 4 factorial with eight replicates. The microbiological analysis revealed the sanitary conditions in which the samples were handled and stored, yielding counts of psychrotrophiles (2.18 x 105 CFU g-1) and mesophiles (2.4 x 105 CFU g-1) well below the critical deterioration level (106 CFU g-1). The pH (5.57) and the loss on cooking (24.13%) were not influenced by the evaluated variables (P > 0.05).The other evaluated parameters significantly varied as a function of the maturation period and the cut thickness (both P < 0.05). Meat luminosity varied with both the cut thickness and maturation period.The 2.5-cm-thick cut matured for 14 days and the 7.5-cm-thick cut matured for 21 days were darker than the 2.5-cm-thick cut matured for 7 days and the 7.5-cm-thick cut matured for 14 days, which were the lighter-colored samples (similar to non-matured meat). The intensity of the red color of the meat was different beginning after 14 days of maturation in the 7.5-cm cuts (P < 0.05) but differences were not evident in any of the 2.5-cm cuts (P > 0.05). Regarding the b* intensity, the 2.5-cm cut yielded a darker staining at time zero, which decreased with the maturation period. However, the 7.5-cm cut differed between the non-matured and the matured samples.[...](AU)

O efeito da maturação nas características físicas (pH, cor, perda de peso na cozedura e força de cisalhamento) e biológico (microbiologia, no que se refere aos mesófilos e psicrotrófilos e comprimento do sarcômero) do músculo Longissimus thoracic lumborum do gado Nelore adulto foi avaliado durante quatro períodos de maturação (0, 7, 14 e 21 dias) e duas espessuras de corte (2,5 e 7,5 cm). Foram adquiridos 64 músculos de Longissimus thoracic lumborum de machos castrados Nelore do Frigorífico Nutrial, Sergipe, Brasil. O estudo foi realizado utilizando um delineamento inteiramente casualizado,correspondente a um fatorial de 2 x 4 com oito repetições. A análise microbiológica revelou as condições sanitárias em que as amostras foram manipuladas e armazenadas, produzindo contagens de psicrotrófilos (2,18 x 105 UFC g-1) e mesófilos (2,4 x 105 UFC g-1) bem abaixo do nível crítico de deterioração (106 UFC g-1). O pH (5,57) e a perda no cozimento (24,13%) não foram influenciados pelas variáveis avaliadas (P > 0,05). Os outros parâmetros avaliados variaram significativamente em função do período de maturação e da espessura do corte (ambos P < 0,05). A luminosidade da carne variou tanto com a espessura do corte quanto com o período de maturação. O corte de 2,5 cm de espessura maturado durante 14 dias e o corte de 7,5 cm de espessura maturado por 21 dias foi mais escuro do que o corte de 2.5 cm de espessura maturado por 7 dias e os 7.5- que eram as amostras de cores mais claras (semelhantes para carne não maturada). A intensidade da cor vermelha da carne foi diferente após 14 dias de maturação nos cortes de 7,5 cm (P < 0,05), mas as diferenças não foram evidentes em nenhum dos cortes de 2,5 cm (P > 0,05). Em relação à intensidade b*, o corte de 2,5 cm produziu uma coloração mais escura no tempo zero, que diminuiu com o período de maturação. No entanto, o corte de 7,5 cm diferiu entre as amostras não maturadas e as maturadas.[...](AU)

Sarcomere structure: the importance of desmin protein in muscle atrophy / Estructura de sarcómera: la importancia de proteína desmina en atrofia muscular

Knowing the ultrastructure of skeletal muscle is critical to understand how it works under normal situation and the disorders caused by extreme or pathological conditions. Sarcomere is the basic structural unit of striated muscle tissue. An important element of sarcomere architecture are the intermediate filaments, including the desmin protein. Desmin protein contributes to maintenance of cell integrity, efficient transmission of force and mechanochemical signaling within the myocyte. Because of this, desmin protein has constantly been a focus of research that investigates its alterations associated to damage and muscle atrophy under different conditions. The purpose of the following literature review is to describe the basic concepts of muscle ultrastructure, emphasizing the desmin protein role under conditions of muscle disuse atrophy and aging.

Conocer la ultraestructura del músculo esquelético es crítico para entender cómo trabaja bajo situaciones normales y en desórdenes causados por condiciones extremas o patológicas. La sarcómera es la unidad de estructura básica del tejido muscular estriado. Elementos importantes en la arquitectura de la sarcómera son los filamentos intermedios, incluyendo la proteína desmina. La proteína desmina contribuye en mantener la integridad celular, la transmisión eficiente de fuerza y la señalización mecanoquímica dentro del miocito. Debido a lo anterior, la proteína desmina ha sido constante foco de investigación en trabajos que estudian sus alteraciones asociadas a daño y atrofia muscular bajo diferentes condiciones. El propósito de la siguiente revisión de la literatura es describir los conceptos básicos de la ultraestructura muscular, enfatizando en el rol de la proteína desmina bajo condiciones de atrofia muscular por desuso y envejecimiento.

Qualitative characteristics of the Longissimus thoracic lumborum muscle of Nellore cattle during different maturation periods / Características qualitativas do Longissimus thoracic lumborum de bovinos Nelore maturado por diferentes períodos

The effect of maturation on the physical (pH, color, weight loss on cooking, and shear force) and biological (microbiology, concerning mesophiles and psychrotrophiles, and sarcomere length) characteristics of the Longissimus thoracic lumborum muscle of adult Nellore cattle was assessed over four maturation periods (0, 7, 14, and 21 days) and two cut thicknesses (2.5 and 7.5 cm). Sixty-four Longissimus thoracic lumborum muscles from castrated Nellore males were purchased from Frigorífico Nutrial, Sergipe, Brazil. The study was performed using a completely randomized design, corresponding to a 2 x 4 factorial with eight replicates. The microbiological analysis revealed the sanitary conditions in which the samples were handled and stored, yielding counts of psychrotrophiles (2.18 x 105 CFU g-1) and mesophiles (2.4 x 105 CFU g-1) well below the critical deterioration level (106 CFU g-1). The pH (5.57) and the loss on cooking (24.13%) were not influenced by the evaluated variables (P > 0.05).The other evaluated parameters significantly varied as a function of the maturation period and the cut thickness (both P 0.05). Regarding the b* intensity, the 2.5-cm cut yielded a darker staining at time zero, which decreased with the maturation period. However, the 7.5-cm cut differed between the non-matured and the matured samples.[...]

O efeito da maturação nas características físicas (pH, cor, perda de peso na cozedura e força de cisalhamento) e biológico (microbiologia, no que se refere aos mesófilos e psicrotrófilos e comprimento do sarcômero) do músculo Longissimus thoracic lumborum do gado Nelore adulto foi avaliado durante quatro períodos de maturação (0, 7, 14 e 21 dias) e duas espessuras de corte (2,5 e 7,5 cm). Foram adquiridos 64 músculos de Longissimus thoracic lumborum de machos castrados Nelore do Frigorífico Nutrial, Sergipe, Brasil. O estudo foi realizado utilizando um delineamento inteiramente casualizado,correspondente a um fatorial de 2 x 4 com oito repetições. A análise microbiológica revelou as condições sanitárias em que as amostras foram manipuladas e armazenadas, produzindo contagens de psicrotrófilos (2,18 x 105 UFC g-1) e mesófilos (2,4 x 105 UFC g-1) bem abaixo do nível crítico de deterioração (106 UFC g-1). O pH (5,57) e a perda no cozimento (24,13%) não foram influenciados pelas variáveis avaliadas (P > 0,05). Os outros parâmetros avaliados variaram significativamente em função do período de maturação e da espessura do corte (ambos P 0,05). Em relação à intensidade b*, o corte de 2,5 cm produziu uma coloração mais escura no tempo zero, que diminuiu com o período de maturação. No entanto, o corte de 7,5 cm diferiu entre as amostras não maturadas e as maturadas.[...]