Meeting Abstract
P1.63 Sunday, Jan. 4 Muscle architecture and spring properties during active shortening MONROY, J.A.; UYENO, T.A.*; NISHIKAWA, K.C.; Northern Arizona University; Northern Arizona University; Northern Arizona University Ted.Uyeno@nau.edu
Active cross-striated muscle recoils elastically during rapid unloading. Previous analyses show that this spring-like property of actively shortening muscle is remarkably similar in vertebrate muscles (mouse soleus, EDL; frog depressor mandibulae, sartorius). Here, we expand our studies to invertebrate cross- and obliquely striated muscles. The cross-striated abdominal extensors and flexors of crayfish are used in rapid locomotory tail flips. The rigidly parallel sarcomere organization that produces the cross-striated muscle pattern suggests functionality similar to vertebrate skeletal muscle. The obliquely striated longitudinal muscle fibers of the earthworm body wall are used in peristaltic locomotion. Here, the sarcomeres are offset, which allows thick filaments to shear relative to each other and generate force over a large range of lengths. If the sarcomere arrangement plays a role in muscle elasticity, we would expect that muscle stiffness and the mechanism(s) for generating elasticity to differ between cross- and obliquely striated muscles. We used load-clamp experiments to measure the displacement of isolated muscles during recoil following sudden drops in load. We then calculated muscle stiffness across a range of muscle forces and lengths. Our results show that, regardless of sarcomere arrangement, all muscles tested respond similarly to changes in load. Muscle displacement increases exponentially as the change in force increases, resulting in non-linear increases in muscle stiffness with load. Thus, the ability to recoil elastically during rapid unloading appears to be a general feature of cross- and obliquely striated muscle in animals. The mechanism of muscle elasticity does not appear to be affected by differences in sarcomere organization. Supported by NSF IOS-0623791, IOS-0732949.
