Meeting Abstract

42.2  Wednesday, Jan. 5  Myosin’s big radial force: axial and radial tensions are similar in contracting muscle. WILLIAMS, CD*; REGNIER, M; DANIEL, TL; Univ. Washington, Seattle; Univ. Washington, Seattle; Univ. Washington, Seattle cdave@uw.edu

During muscle contraction, cross-bridges attach to thin filaments and generate axial force. At the same time, two other critical mechanical events occur: (1) as muscles shorten, the lattice of filaments dilates and (2) cross-bridges generate tension in the radial direction, in addition to the well-described generation of axial tension. Moreover, radial tension and stiffness in muscle has important functional effects during locomotion. However, all existing computational models of muscle force generation by cross-bridges neglect radial forces, choosing instead to represent myosin as a single extensional spring acting parallel to the long axis of the myofilaments and capable of generating only axial forces. Recent molecular structural evidence shows that myosin moves in more than one direction. To explore these issues, we developed a computational model of cross-bridges in which we consider both axial and radial components of the forces generated by single myosin heads. We created models consisting of both extensional and torsional (watch-like) springs that are based on existing 3D structural reconstructions of myosin. We found that as the radial spacing of the myofilament lattice increases, an attached cross-bridge produces more axial force in the direction of shortening and more compressive radial force, but with decreasing likelihood of interaction. The radial forces are comparable in magnitude to axial forces at all lattice spacings, typically ranging from 10% to 80% of the axial force at small displacements. When these model cross-bridges are placed on a simulated myofilament, their radial force at full activation is maximized near the rest lattice spacing and falls off as lattice spacing diverges from rest conditions.