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

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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.