Meeting Abstract
Muscle is a unique material which is capable of performing many different functions, acting as a spring, motor, brake, or strut as characterized by a workloop, a periodically activated force-length curve. What properties of muscle allow for muscle workloop variation? While many determinants of muscle workloops are known (the classic force-length, force-velocity, and twitch response), previous work (Ahn et al., 2006) has identified two muscles in B. discoidalis which have nearly identical classical determinants of workloop behavior, but have different workloops. Yet to be examined is the microstructure of these muscles and their relationship to workloops. This can be studied by using x-ray diffraction to measure the spacing and arrangement of myosin and actin under physiological conditions. Using the BioCAT x-ray beamline at the Advanced Photon Source at Argonne NL, we studied the lattice structure of both muscles passively stretched under physiological strains. We first examined their packing structures and determined them to be identical for these muscles. We also found that one muscle’s inter-myosin spacing was 1 nm larger than the other’s. The largest spacing difference was at high strain, where activation occurs in vivo. This is significant because in these muscles’ workloops, despite simultaneous activation, the time course of force production following activation is different. Since lattice spacing affects the dynamics of the molecular motors responsible for force production, it’s reasonable that lattice spacing changes could be responsible for variation in workloops for these muscles. Previous experimental work (George et al., 2013) and computational models (Williams et al., 2010) suggest even 1 nm lattice spacing differences can be significant in determining muscle work output.
