RUI: Molecular Mechanisms for Physiological Variations in the Swimming Musculature of Fishes

鱼类的轴向游动是由肌瘤驱动的，这种肌肉组织通常构成了动物身体的大部分。肌组由红色或有氧肌纤维和白色或无氧肌纤维组成，白色肌肉通常占游泳肌肉组织的90%，红色肌肉占10%或更少。缓慢而稳定的游泳是由沿着动物两侧的红色肌肉提供动力的。肌肉收缩的交替波从头部传递到尾部的红色肌肉，导致身体和/或尾巴的摆动，从而产生向前推力。在过去的十年中，对红肌或有氧肌在稳定、轴向游泳中的功能的研究已经揭示了各种各样的能量产生模式。在某些鱼类中，每个纵向位置产生的游泳动力相等（例如鳗鱼、鲭鱼和金枪鱼），而其他鱼类从理论上讲可以从前肌肌体产生更高的机械动力（例如鲤鱼）。最后，一些物种已经被证明主要是通过后肌肌瘤来为游泳提供动力（如鲫鱼、虹鳟鱼和鲈鱼）。在大多数被研究的物种中，与后肌相比，前肌瘤经历较低的肌肉劳损，较长的激活周期和较短的肌肉激活相移，相对于肌肉缩短。这些肌肉活动条件限制了前肌瘤在稳定游泳时产生的力量。然而，红肌的收缩动力学也随着大多数鱼类的长度而变化，这些收缩特性的变化可以减轻不利激活条件的影响。例如，更快的动力学（如放松速率和某些物种的激活速率）允许前肌在给定的激活条件下比后肌产生更多的能量。这项研究计划的目标是了解不同鱼类游泳形式变化的基础。该建议侧重于分子和肌肉生理学水平，并解决收缩动力学与肌肉蛋白质组成的关系。由于理解游泳过程中力量产生的模式需要了解该肌肉的动力学，我建议测量鱼红肌肉的收缩动力学，并确定动力学纵向变化的分子相关性。该提案将追求两个目标。首先，虹鳟鱼游泳肌肉组织生理变化的分子机制是什么？几种分子技术将用于确定先前观察到的收缩动力学和动力产生的纵向变化是否与游泳肌分子结构的变化有关。分子技术将用于筛选鳟鱼的有氧游泳肌肉，以观察激活和放松速率的纵向差异是否与肌肉蛋白质组成的变化相关。几种肌肉蛋白将被靶向，包括肌钙蛋白、原肌凝蛋白和肌凝蛋白。第二，红肌的分子变异模式是否因物种而异？鱼类的轴向游泳有很大的不同，从金枪鱼和鲭鱼的硬体游泳到游泳的鳗鱼的高身体曲率。这项研究计划将收缩动力学和分子结构的分析扩展到几个在游泳模式和动力产生模式上有所不同的新物种。很少知道的模式的收缩动力学和肌肉组成之间的鱼类一般。为了达到这个目的，将使用相同种类的分子方法。然而，肌肉收缩特性的生理测量也将被进行，包括激活和松弛速率以及缩短速度的测量。目标物种包括鳗鱼、鲭鱼、大口黑鲈和鲹。

Axial swimming in fishes is powered by the myotome, the musculature that usually constitutes the majority of the animal's mass. The myotome is composed of both red or aerobic muscle fibers and white or anaerobic muscle fibers, with the white muscle often comprising 90% and red muscle 10% or less of the swimming musculature. Slow, steady swimming is powered by the lateral strips of red muscle that run down each side of the animal. Alternating waves of muscular contraction pass down the red muscle from head to tail, leading to oscillation of the body and/or tail and resulting in forward thrust. Research over the last decade on the function of red or aerobic muscle during steady, axial swimming has revealed a variety of patterns of power production. In some fish species, the power for swimming is generated in equal amounts by each longitudinal position (e.g. eels, mackerel and tuna), while others are theorized to generate much higher mechanical power from the anterior myotome (e.g. carp). Lastly, several species have been shown to power swimming primarily with the posterior myotome (e.g. scup, rainbow trout and bass). In most of the species studied the anterior myotome experiences lower muscle strains, longer activation periods and shorter phase shifts of muscle activation relative to muscle shortening, as compared to posterior muscle. These muscle activity conditions limit power production by the anterior myotome during steady swimming. However, the contraction kinetics of the red muscle also vary along the length of most fishes, and these variations in the contractile properties can mitigate the impact of disadvantageous activation conditions. For instance, faster kinetics (e.g. rates of relaxation and, in some species, rates of activation) allows anterior muscle to produce more power under a given set of activation conditions than posterior muscle. The goal of this research program is to understand the basis for variations in swimming form in different fish species. This proposal focuses at the molecular and muscle physiology levels and addresses the relationship of contraction kinetics to the protein composition of muscle. Since understanding the patterns of power production during swimming requires knowledge of the kinetics of that muscle, I propose to measure the contraction kinetics of fish red muscle and to determine the molecular correlates of longitudinal variations in kinetics. The proposal will pursue two objectives.First, what are the molecular mechanisms for physiological variations in the swimming musculature of rainbow trout? Several molecular techniques will be used to determine if previously observed longitudinal variations in contraction kinetics and power production are associated with variations in the molecular structure of swimming muscle. Molecular techniques will be developed to screen the aerobic swimming muscle of trout to see if longitudinal differences in both activation and relaxation rates correlate with variations in the protein composition of the muscle. Several muscle proteins will be targeted, including troponin, tropomyosin and myosin. Second, do the patterns of molecular variation in the red muscle vary between species? Axial based swimming in fishes varies widely, from stiff-bodied swimming in tuna and mackerel to the high body curvature of swimming eels. This research proposal extends the analysis of both contraction kinetics and molecular structure to several new species that vary in swimming mode and patterns of power production. Little is known of the patterns of contraction kinetics and muscle composition amongst fishes in general. For this objective, the same sorts of molecular approaches will be used. However, physiological measurements of muscle contractile properties will also be made, including measurements of activation and relaxation rates and shortening velocity. The targeted species include eel, mackerel, largemouth bass and scup.