A fibra muscular e fatores que interferem no seu fenótipo / The muscle fiber and the factors that interfere with its phenotype

O grande interesse atual em tirar proveito das variações na performance humana, nos levam a busca do entendimento as adaptações fisiológicas, bioquímicas e morfológicas nos tecidos envolvidos. Os resultados obtidos através de modelos experimentais fornecem informações para melhor entender a função muscular, e com isso permitir planejar um treinamento adequado ao objetivo pretendido, tendo como base adaptações fisiológicas. A performance esportiva depende de um grande número de fatores, o tipo do músculo e os estímulos a que ele é submetido e são sem dúvida parâmetros importantes para o desempenho atlético. Para cada modalidade é ideal ter um grupo de fibras predominante adequado às características específicas da atividade. Dependendo do tipo de estímulo podemos obter um aumento de força, sendo esta adaptação uma das mais importantes para a manutenção da saúde ou a melhora do desempenho atlético.

Diversity and plasticity of vertebrate skeletal muscle: insights from hybrid fibres

It is now generally accepted that hybrid skeletal muscle fibres are not experimental artefacts, but complex molecular systems that expand the functional repertoire of the muscle to which they belong. The purpose of this review is to highlight the cognitive value of hybrid fibres by discussing several insights into skeletal muscle biology produced by studies using hybrid fibres and/or muscles containing hybrid fibres. There is strong evidence that hybrid fibres can be used as indicators of muscle remodeling and specialization. Also, there is increasing evidence that hybrid fibres are suitable for investigating issues related to (i) the coexpression of different myosin heavy chain (MHC) isoforms and their assembly in the sarcomeric structure, (ii) the operation of the muscle cell as a multinuclear system, (iii) the tightness of the relationship between MHC isoform expression and expression of other polymorphic muscle proteins, (iv) the tightness of the relationship between MHC isoform expression and various contractile parameters, and (v) the extent of the neural input into defining the molecular and functional phenotype of skeletal muscle cells. It is predicted that, when used together with imaginatively designed methods, the hybrid fibres will further our (still limited) understanding of the regulation of muscle gene expression in multinuclear cells and of the interactions of gene products within and across different intracellular signalling pathways.

Eucalyptol, an essential oil, reduces contractile activity in rat cardiac muscle

Eucalyptol is an essential oil that relaxes bronchial and vascular smooth muscle although its direct actions on isolated myocardium have not been reported. We investigated a putative negative inotropic effect of the oil on left ventricular papillary muscles from male Wistar rats weighing 250 to 300 g, as well as its effects on isometric force, rate of force development, time parameters, post-rest potentiation, positive inotropic interventions produced by Ca2+ and isoproterenol, and on tetanic tension. The effects of 0.3 mM eucalyptol on myosin ATPase activity were also investigated. Eucalyptol (0.003 to 0.3 mM) reduced isometric tension, the rate of force development and time parameters. The oil reduced the force developed by steady-state contractions (50 percent at 0.3 mM) but did not alter sarcoplasmic reticulum function or post-rest contractions and produced a progressive increase in relative potentiation. Increased extracellular Ca2+ concentration (0.62 to 5 mM) and isoproterenol (20 nM) administration counteracted the negative inotropic effects of the oil. The activity of the contractile machinery evaluated by tetanic force development was reduced by 30 to 50 percent but myosin ATPase activity was not affected by eucalyptol (0.3 mM), supporting the idea of a reduction of sarcolemmal Ca2+ influx. The present results suggest that eucalyptol depresses force development, probably acting as a calcium channel blocker.