RESUMO
O experimento foi realizado com o objetivo de comparar as características de carcaça e da carne de 18 novilhas dos cruzamentos comerciais: ½ Nelore ½ Limousin (L), ½ Limousin » Red Angus » Nelore (LR), e ⅝ Red Angus ⅜ Nelore (RNR). As novilhas foram confinadas aos 18 meses de idade, com média de peso de 280 ± 8,4 kg, durante 112 dias. Após o abate e resfriamento das carcaças foram avaliados: rendimento (RC), área de olho de lombo (AOL), espessura de coxão (EC), cobertura de gordura (CG), comprimento de carcaça e perna, percentagem de músculo, ossos e gordura. Das amostras do Longissimus dorsi foram analisados a composição centesimal, o pH, a perda de água, a força de cisalhamento (FC), o comprimento de sarcômero (CS) e o índice de fragmentação miofibrilar (IFM). Os dados obtidos foram submetidos à análise de variância, e as médias comparadas pelo teste de Tukey a 5% de significância. O cruzamento LR apresentou as melhores características de carcaça e de carne com 54,72% de RC; 27,87 cm de EC; 4,53 cm de CG; 63,65 cm2 de AOL; 64,58% de carne magra; 26,63% de perda de água; pH de 5,72; 2,49 kg de FC; 1,91 microm de CS; e 83,59 de IFM.
The experiment was carried out with the objective of comparing carcass and meat characteristics of 18 heifers from the following industrial crossbreeds: ½ Nelore ½ Limousin (L), ½ Limousin » Red Angus » Nelore (LR), and ⅝ Red Angus ⅜ Nelore (RNR). The heifers were confined at 18 months of age, weighing 280 ± 8.4 kg, during 112 days. After slaughter and carcass cooling, the following traits were evaluated: carcass yield (CY); rib eye area (REA); cushion thickness (CT); fat thickness (FT); carcass length (CL) and leg length (LL); muscle, bone and fat percentages. From Longissimus dorsi muscle samples, the following traits were evaluated: aproximate composition; pH; water loss; shear force (SF); sarcomere length (SL); myofibril fragmentation index (MFI). The data were submitted to analysis of variance and the means were compared by Tukeys test at 5% significance. The LR crossbreed showed the best carcass and meat characteristics, with CY=54.72%, CT=27.87 cm, FT=4.53 cm, REA=63.65 cm2, lean meat=64.58%, water loss=26.63%, pH=5.72; SF=2.49 kg, SL=1.91 microm and MFI=83.59.
Assuntos
Animais , Bovinos , Carne/análise , Peso Corporal/genética , Miofibrilas/fisiologia , Sarcômeros/fisiologiaRESUMO
O experimento foi realizado com o objetivo de comparar as características de carcaça e da carne de 18 novilhas dos cruzamentos comerciais: ½ Nelore ½ Limousin (L), ½ Limousin » Red Angus » Nelore (LR), e ⅝ Red Angus ⅜ Nelore (RNR). As novilhas foram confinadas aos 18 meses de idade, com média de peso de 280 ± 8,4 kg, durante 112 dias. Após o abate e resfriamento das carcaças foram avaliados: rendimento (RC), área de olho de lombo (AOL), espessura de coxão (EC), cobertura de gordura (CG), comprimento de carcaça e perna, percentagem de músculo, ossos e gordura. Das amostras do Longissimus dorsi foram analisados a composição centesimal, o pH, a perda de água, a força de cisalhamento (FC), o comprimento de sarcômero (CS) e o índice de fragmentação miofibrilar (IFM). Os dados obtidos foram submetidos à análise de variância, e as médias comparadas pelo teste de Tukey a 5% de significância. O cruzamento LR apresentou as melhores características de carcaça e de carne com 54,72% de RC; 27,87 cm de EC; 4,53 cm de CG; 63,65 cm2 de AOL; 64,58% de carne magra; 26,63% de perda de água; pH de 5,72; 2,49 kg de FC; 1,91 microm de CS; e 83,59 de IFM.(AU)
The experiment was carried out with the objective of comparing carcass and meat characteristics of 18 heifers from the following industrial crossbreeds: ½ Nelore ½ Limousin (L), ½ Limousin » Red Angus » Nelore (LR), and ⅝ Red Angus ⅜ Nelore (RNR). The heifers were confined at 18 months of age, weighing 280 ± 8.4 kg, during 112 days. After slaughter and carcass cooling, the following traits were evaluated: carcass yield (CY); rib eye area (REA); cushion thickness (CT); fat thickness (FT); carcass length (CL) and leg length (LL); muscle, bone and fat percentages. From Longissimus dorsi muscle samples, the following traits were evaluated: aproximate composition; pH; water loss; shear force (SF); sarcomere length (SL); myofibril fragmentation index (MFI). The data were submitted to analysis of variance and the means were compared by Tukeys test at 5% significance. The LR crossbreed showed the best carcass and meat characteristics, with CY=54.72%, CT=27.87 cm, FT=4.53 cm, REA=63.65 cm2, lean meat=64.58%, water loss=26.63%, pH=5.72; SF=2.49 kg, SL=1.91 microm and MFI=83.59.(AU)
Assuntos
Animais , Bovinos , /genética , Peso Corporal/genética , Carne/análise , Sarcômeros/fisiologia , Miofibrilas/fisiologiaRESUMO
The cardiac lethal mutation in Mexican axolotl (Ambystoma mexicanum) results in a lack of contractions in the ventricle of mutant embryos. Previous studies have demonstrated that tropomyosin, a component of thin filaments, is greatly reduced in mutant hearts lacking myofibril organization. Confocal microscopy was used to examine the structure and comparative amount of tropomyosin at heartbeat initiation and at a later stage. The formation of functional sarcomeres coincided with contractions in normal hearts at stage 35. A-bands and I-bands were formed at stage 35 and did not change at stage 39. The widening of Z-bodies into z-lines was the main developmental difference between stage 35 and 39 normal hearts. Relative to normal hearts, a reduction of sarcomeric protein levels in mutant hearts at stage 35 was found, and a greater reduction occurred at later stages. The lower level of tropomyosin limited the areas where organized myofibrils formed in the mutant. The areas that had tropomyosin staining also had staining for alpha-actinin and myosin. Early myofibrils formed in these areas but the A-bands and I-bands were shorter than normal. At a later stage in the mutant, A-bands and I-bands remained shorter and importantly the Z-bodies also did not form wider z-lines.
Assuntos
Genes Letais/fisiologia , Cardiopatias/genética , Mutação/fisiologia , Sarcômeros/fisiologia , Tropomiosina/genética , Tropomiosina/fisiologia , Actinina/genética , Actinina/fisiologia , Ambystoma mexicanum , Animais , Embrião não Mamífero , Imunofluorescência , Coração/fisiologia , Microscopia Confocal , Miofibrilas/fisiologia , Miofibrilas/ultraestrutura , Sarcômeros/ultraestrutura , Fixação de TecidosRESUMO
The Mexican axolotl, Ambystoma mexicanum, has been a useful animal model to study heart development and cardiac myofibrillogenesis. A naturally-occurring recessive mutant, gene "c", for cardiac non-function in the Mexican axolotl causes a failure of myofibrillogenesis due to a lack of tropomyosin expression in homozygous mutant (c/c) embryonic hearts. Myofibril-inducing RNA (MIR) rescues mutant hearts in vitro by promoting tropomyosin expression and myofibril formation thereafter. We have studied the effect of MIR on the expression of various isoforms of cardiac troponin T (cTnT), a component of the thin filament that binds with tropomyosin. Four alternatively spliced cTnT isoforms have been characterized from developing axolotl heart. The expression of various cTnT isoforms in normal, mutant, and mutant hearts corrected with MIR, is evaluated by real-time RT-PCR using isoform specific primer pairs; MIR affects the total transcription as well as the splicing of the cTnT in axolotl heart.
Assuntos
Ambystoma mexicanum/embriologia , Coração/embriologia , Miocárdio/metabolismo , Miofibrilas/fisiologia , RNA/metabolismo , Troponina T/genética , Troponina T/metabolismo , Ambystoma mexicanum/genética , Animais , Animais Geneticamente Modificados , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Coração/fisiologia , RNA/genética , Relação Estrutura-AtividadeRESUMO
Strength and flexibility are common components of exercise programmes; however, it is not clear how best to include both of these elements in a single training programme. It is common practice among athletes, coaches and recreational exercisers to perform a stretching routine before a strength training session. Stretching exercises are regularly recommended, even in many textbooks, with the claimed purpose of preventing injury and muscle soreness, or even enhancing performance. However, as highlighted in recent review articles, this recommendation lacks scientific evidence. Thus, the purpose of the present review is to determine the acute and chronic effects of stretching on strength performance, together with the underlying mechanisms. Although most studies have found acute decreases in strength following stretching, and that such decreases seem to be more prominent the longer the stretching protocol, the number of exercises and sets, and the duration of each set have, in general, exceeded the ranges normally recommended in the literature. Consequently, the duration of the stimuli were excessively long compared with common practice, thus making evident the need for further studies. In addition, when recommending flexibility exercises, one should consider other underlying issues, such as the safety of the participants, possible increases in injury risks and the unnecessary time expenditure. Many mechanisms underlying stretching exercises still demand investigation so that links between the observed effects, their causes and the consequences may be constructed.
Assuntos
Força Muscular/fisiologia , Exercícios de Alongamento Muscular , Adaptação Fisiológica , Animais , Elasticidade , Humanos , Fator de Crescimento Insulin-Like I/fisiologia , Neurônios Motores/fisiologia , Contração Muscular/fisiologia , Miofibrilas/fisiologiaRESUMO
In the axolotl, Ambystoma mexicanum, a simple, recessive cardiac-lethal mutation in gene "c" results in the hearts of c/c homozygous animals being deficient in sarcomeric tropomyosin (TM) and failing to form mature myofibrils. Subsequently, the mutant hearts do not beat. A three-step model of myofibril assembly recently developed in cell culture prompted a reassessment of the myofibril assembly process in mutant hearts using a relatively new late marker for thin filament assembly, tropomodulin (Tmod). This is, to the best of our knowledge, the first report of tropomodulin in an amphibian system. Tropomodulin antibodies were immunolocalized to the ends of the thin filaments. Tropomodulin was also found in discrete punctate spots in normal and mutant hearts, often in linear arrays suggestive of early myofibril formation. The tropomodulin spots assessed in stage 41/42 mutant hearts co-localized with antibodies to other myofibrillar proteins indicative of nascent myofibril formation. This suggests a failure of elongation/maturation of nascent myofibrils, which could be a consequence of decreased TM levels or increased Tmod/ TM ratio. Unlike tropomyosin, there is no apparent decrease in the level of Tmod expression in mutant hearts.
Assuntos
Genes Letais/genética , Coração/crescimento & desenvolvimento , Miocárdio/metabolismo , Tropomodulina/biossíntese , Tropomodulina/genética , Ambystoma , Animais , Anticorpos Monoclonais , Biomarcadores , Western Blotting , Eritrócitos/metabolismo , Imuno-Histoquímica , Microscopia Confocal , Mutação/fisiologia , Miofibrilas/patologia , Miofibrilas/fisiologia , Tropomodulina/deficiênciaRESUMO
Ambystoma mexicanum is an intriguing animal model for studying heart development because it carries a mutation in gene c. Hearts of homozygous recessive (c/c) mutant embryos do not contain organized myofibrils and fail to beat. The defect can be corrected by organ-culturing the mutant heart in the presence of RNA from anterior endoderm or endoderm/mesoderm-conditioned medium. By screening a cDNA library made of total conditioned medium RNA from normal axolotl embryonic endoderm, we isolated a single clone (MIR), the synthetic RNA from which corrects the mutant heart defect by promoting myofibrillogenesis and thus was named MIR (myofibrillogenesis inducing RNA). In the present study, we have examined MIR gene expression in mutant axolotl hearts at early pre-heart-beat developmental stages and found its quantitative expression, as detected by RT-PCR, to be the same as in normal hearts. However, careful analysis of sequence data revealed a G-->U point mutation in the mutant MIR RNA. Further computational analyses, using GENEBEE software to compare normal and mutant MIR RNAs show a significant alteration in RNA secondary structure of the point-mutated MIR RNA. The results from bioassay and confocal microscopy immunofluorescent studies demonstrate that, unlike MIR RNA derived from normal embryos, the mutated MIR RNA does not promote myofibrillogenesis in mutant embryonic hearts and fails to rescue/correct the mutant heart defect.
Assuntos
Ambystoma mexicanum/embriologia , Regulação da Expressão Gênica no Desenvolvimento , Coração/embriologia , Desenvolvimento Muscular/fisiologia , RNA/farmacologia , Animais , Sequência de Bases , Biblioteca Gênica , Cardiopatias Congênitas/veterinária , Microscopia Confocal , Dados de Sequência Molecular , Miofibrilas/fisiologia , Técnicas de Cultura de Órgãos , Mutação Puntual , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
In the catalytic cycle of skeletal muscle, myosin alternates between strongly and weakly bound cross-bridges, with the latter contributing little to sustained tension. Here we describe the action of DMSO, an organic solvent that appears to increase the population of weakly bound cross-bridges that accumulate after the binding of ATP, but before P(i) release. DMSO (5-30%, v/v) reversibly inhibits tension and ATP hydrolysis in vertebrate skeletal muscle myofibrils, and decreases the speed of unregulated F-actin in an in vitro motility assay with heavy meromyosin. In solution, controls for enzyme activity and intrinsic tryptophan fluorescence of myosin subfragment 1 (S1) in the presence of different cations indicate that structural changes attributable to DMSO are small and reversible, and do not involve unfolding. Since DMSO depresses S1 and acto-S1 MgATPase activities in the same proportions, without altering acto-S1 affinity, the principal DMSO target apparently lies within the catalytic cycle rather than with actin-myosin binding. Inhibition by DMSO in myofibrils is the same in the presence or the absence of Ca(2+) and regulatory proteins, in contrast with the effects of ethylene glycol, and the Ca(2+) sensitivity of isometric tension is slightly decreased by DMSO. The apparent affinity for P(i) is enhanced markedly by DMSO (and to a lesser extent by ethylene glycol) in skinned fibres, suggesting that DMSO stabilizes cross-bridges that have ADP.P(i) or ATP bound to them.