Measurement of the OHC lateral membrane
using an atomic force microscope

English / Japanese


　 It has been established that the isolated outer hair cell (OHC) can elongate and contract in response to changes in the membrane potential. The OHC motility is considered to be due to the deformation of the motor protein, which is distributed along the lateral wall of the OHC (Fig. 1), and it is thought that the vibration of the basilar membrane is amplified by the force which accompanies the motility of the OHC. To understand this amplification, it is important to know the structure and mechanical properties of the OHC lateral wall, because the mechanism of the motility is related to the OHC lateral wall. However, these factors have not been clarified. In this study, therefore, an attempt was made to measure the ultrastructure of the OHC lateral membrane under physiological conditions using an atomic force microscope (AFM) (Fig. 2). Figure 3 shows one of the results. From this image, the lattice formed by some differently oriented domains can be discerned. Within each domain, the circumferential filaments are cross-linked by thinner filaments, and these circumferential filaments and cross-links would respectively be actin filaments and spectrin, which are parts of the cortical lattice. As the next step in this study, we intend to measure the ultrastructure of the lateral wall in detail and identify the mechanism of motility.





Fig. 1.　Structure of the OHC lateral membrane.
　






Fig. 2.　Measurement system.
The system consists of an atomic force microscope (AFM) and an inverted microscope in a sound-proof chamber. As the AFM unit is mounted on the inverted microscope, it is possible to observe samples with the inverted microscope and the AFM at the same time.






Fig. 3.　An AFM images of the lateral surface in the middle region of OHC.
  1. The position of the scanning area.
  2. The AFM image which is obtained at the red area in (a). The scanning area is 1.0 mm×1.0 mm. The lattice formed by some differently oriented domains is recognized. Within each domain, the circumferential filaments are cross-linked by thinner filaments, and these circumferential filaments and cross-links would respectively be actin filaments and spectrin, which are parts of the cortical lattice.
  3. A schematic of the domains and filaments in (b). Boundary lines of domains, circumferential filaments and cross-links are shown by dotted lines, thick solid lines and thin solid lines, respectively.



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