M. Ulfendahl et al., AXIAL AND TRANSVERSE STIFFNESS MEASURES OF COCHLEAR OUTER HAIR-CELLS SUGGEST A COMMON MECHANICAL BASIS, Pflugers Archiv, 436(1), 1998, pp. 9-15
The function of the hearing organ is based on mechanical processes occ
urring at the cellular level. The mechanical properties of guinea-pig
isolated sensory cells were investigated using two different technique
s. The stiffness of the outer hair cells along the longitudinal axis w
as measured by compressing the cell body using stiffness-calibrated qu
artz fibres. For cells with a mean length of 69 mu m, the mean axial c
ompression stiffness was 1.1+/-0.8 mN/m (+/-SD). There was an inverse
relation between stiffness and cell length. The stiffness of the cell
membrane perpendicular to the longitudinal axis of the sensory cell wa
s measured by indenting the cell membrane with a known force. The mean
lateral indentation stiffness was 3.3+/-1.5 mN/m (+/-SD) for cells wi
th a mean length of 64 mu m. Longer cells were less stiff than short c
ells. Modelling the hair cell as a shell with bending resistance, fini
te element calculations demonstrated that the axial compression stiffn
ess correlated well with the lateral indentation stiffness, and that a
simple isotropic model is sufficient to explain the experimental obse
rvations despite the different stress strain states produced by the tw
o techniques. The results imply that the two different stiffness prope
rties may originate from the same cytoskeletal structures. It is sugge
sted that the mechanical properties of the outer hair cells are design
ed to influence the sound-induced motion of the reticular lamina. In s
uch a system, stiffness changes of the outer hair cell bodies could ac
tively control the efficiency of the mechanical coupling between the b
asilar membrane and the important mechanoelectrical transduction sites
at the surface of the hearing organ.