9600840 Marden This research investigates the locomotor physiology of a model organism at molecular through cellular, organismal, and ecological levels, and will demonstrate how effects at one level interact with effects at other levels. In so doing, the research would lead to a novel understanding of mechanistic and evolutionary processes that govern performance physiology of muscle. Dragonflies (Libellula pulchella) undergo a dramatic change in flight performance and thermal sensitivity of muscle function during adult maturation. Preliminary data suggest that the mechanism underlying this developmental transition is a tenfold increase in calcium sensitivity of muscle activation, which appears to be caused by a change in isoform expression of the calcium regulatory protein troponin-t. The investigators will use recombinant troponin-t to perform isoform extraction/replacement experiments that will experimentally demonstrate the role that age-specific troponin-t isoforms play in determining calcium sensitivity of muscle activation. These experiments will provide some of the first data that address the specific cellular role of troponin-t isoform variation. Troponin-t isoform shifts occur during muscle development in many types of animals (including humans), as well as human heart muscle during cardiac arrest and recovery from cardiac arrest. Mutations in troponin-t cause, by mechanisms presently unknown, an inherited heart disease in humans (hypertrophic cardiac myopathy). Thus, the results will have general andpotentially even clinical value. Preliminary data also indicate that changes in calcium sensitivity of muscle activation affect the timing and force generation of muscle twitch contractions, which in turn may cause changes in the energy efficiency of locomotion. The researchers will test this prediction by determ ining how energy efficiency of flight varies with age and muscle maturation. They will perform parallel experiments with distantly related dragonflies that show similar and dissimilar patterns of muscle maturation in order to determine if the results allow accurate predictions that can be extended to other species.
