title: Local mechanical properties of mouse outer hair cells: atomic force microscopic study.
abstract: OBJECTIVE
  Outer hair cells (OHCs) are capable of altering their cell length in response to changes in membrane potential. Due to this electromotility, OHCs probably subject the basilar membrane to force, resulting in cochlear amplification. To understand the mechanism of such amplification, knowledge of the mechanical properties of OHCs is required since the force produced by OHC electromotility is thought to depend on such properties. Various studies have been conducted to investigate the mechanical properties of guinea pig OHCs. With regard to mice, however, although various kinds of transgenic and knockout mice possess great potential as research models, the mechanical properties of mouse OHCs have not as yet been reported since the cells and/or tissues in the mouse hearing organ are relatively small and vulnerable to external stimuli, rendering sample preparation difficult. In this study, therefore, to establish indicators of the mechanical properties of OHCs in mice, such properties were measured by atomic force microscopy (AFM).
  
  
  METHODS
  CBA/JNCrj strain male mice aged 10-12 weeks (25-30 g) were used. Cochleae were dissected out from the animal and both the basilar membrane and the organ of Corti were simultaneously unwrapped from the modiolus with forceps. Dissected coiled tissue was then incubated with an enzymatic digestion medium for 15 min. After digestion, OHCs were isolated by gently triturating the coiled tissue. Local mechanical properties of the OHCs were then measured by an indentation test using an AFM.
  
  
  RESULTS
  Young's modulus and stiffness of the OHC in the apical turn of the mouse cochlea were 2.1+/-0.5 kPa and 4.4+/-1.2 mN/m, respectively.
  
  
  CONCLUSIONS
  Young's modulus of the OHC in the apical turn of the cochlea in mice was roughly the same as that in the apical turn of the cochlea in guinea pigs; however, the stiffness of the former was about two times greater than that of the latter because the cell length of the former was shorter than that of the latter.
authors.affiliation: Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai 980-8579, Japan. michio@wadalab.mech.tohoku.ac.jp
authors.forename: Michio
authors.initials: M
authors.lastname: Murakoshi
authors.forename: Naohiro
authors.initials: N
authors.lastname: Yoshida
authors.forename: Koji
authors.initials: K
authors.lastname: Iida
authors.forename: Shun
authors.initials: S
authors.lastname: Kumano
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Wada
mesh_terms: D000818:Animals; D001489:Basilar Membrane / Q000166:cytology / Q000502:physiology; D001696:Biomechanical Phenomena; D003051:Cochlea / Q000166:cytology / Q000502:physiology; D018072:Hair Cells, Auditory, Outer / Q000166:cytology* / Q000502:physiology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018625:Microscopy, Atomic Force / Q000295:instrumentation*; D008954:Models, Biological