title: Role for stress fiber contraction in surface tension development and stretch-activated channel regulation in C2C12 myoblasts.
abstract: Membrane-cytoskeleton interaction regulates transmembrane currents through stretch-activated channels (SACs); however, the mechanisms involved have not been tested in living cells. We combined atomic force microscopy, confocal immunofluorescence, and patch-clamp analysis to show that stress fibers (SFs) in C2C12 myoblasts behave as cables that, tensed by myosin II motor, activate SACs by modifying the topography and the viscoelastic (Young's modulus and hysteresis) and electrical passive (membrane capacitance, C(m)) properties of the cell surface. Stimulation with sphingosine 1-phosphate to elicit SF formation, the inhibition of Rho-dependent SF formation by Y-27632 and of myosin II-driven SF contraction by blebbistatin, showed that not SF polymerization alone but the generation of tensional forces by SF contraction were involved in the stiffness response of the cell surface. Notably, this event was associated with a significant reduction in the amplitude of the cytoskeleton-mediated corrugations in the cell surface topography, suggesting a contribution of SF contraction to plasma membrane stretching. Moreover, C(m), used as an index of cell surface area, showed a linear inverse relationship with cell stiffness, indicating participation of the actin cytoskeleton in plasma membrane remodeling and the ability of SF formation to cause internalization of plasma membrane patches to reduce C(m) and increase membrane tension. SF contraction also increased hysteresis. Together, these data provide the first experimental evidence for a crucial role of SF contraction in SAC activation. The related changes in cell viscosity may prevent SAC from abnormal activation.
authors.affiliation: Department of Physics, Centro Studi Dinamiche Complesse, University of Florence, Florence, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Sbrana
authors.forename: Chiara
authors.initials: C
authors.lastname: Sassoli
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Meacci
authors.forename: Daniele
authors.initials: D
authors.lastname: Nosi
authors.forename: Roberta
authors.initials: R
authors.lastname: Squecco
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Paternostro
authors.forename: Bruno
authors.initials: B
authors.lastname: Tiribilli
authors.forename: Sandra
authors.initials: S
authors.lastname: Zecchi-Orlandini
authors.forename: Fabio
authors.initials: F
authors.lastname: Francini
authors.forename: Lucia
authors.initials: L
authors.lastname: Formigli
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D003599:Cytoskeleton / Q000502:physiology; D005455:Fluorescent Antibody Technique; D015640:Ion Channel Gating; D007473:Ion Channels / Q000096:biosynthesis / Q000502:physiology*; D040542:Mechanotransduction, Cellular; D051379:Mice; D018625:Microscopy, Atomic Force; D018613:Microscopy, Confocal; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D032448:Myoblasts, Skeletal / Q000502:physiology* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D022502:Stress Fibers / Q000502:physiology*; D013314:Stress, Mechanical; D013500:Surface Tension; D014783:Viscosity
chemical_list: D007473:Ion Channels; D002118:Calcium