Current evidence suggests that the adaptation motor of mechanoelectrical transduction in vertebrate hair cells is myosin-Iβ. Previously, confocal and electron microscopy of bullfrog saccular hair cells using an anti-myosin-Iβ antibody labeled the tips of stereocilia. We have now done quantitative immunoelectron microscopy to test whether myosin-Iβ is enriched at or near the side plaques of tip links, the proposed sites of adaptation, using hair bundles that were serially sectioned parallel to the macular surface. The highest particle density occurred at stereocilia bases, close to the cuticular plate. Also, stereocilia of differing lengths had approximately the same number of total particles, suggesting equal targeting of myosin-Iβ to all stereocilia. Finally, particles tended to clump in clusters of two to five particles in the distal two-thirds of stereocilia, suggesting a tendency for self-assembly of myosin-Iβ. As expected from fluorescence microscopy, particle density was high in the distal 1 μm of stereocilia. If myosin-Iβ is the adaptation motor, a difference should exist in particle density between regions containing the side plaque and those excluding it. Averaging of particle distributions revealed two regions with approximately twice the average density: at the upper ends of tip links in a 700-nm-long region centered ~100 nm above the side plaque, and at the lower ends of tip links within the tip plaques. Controls demonstrated no such increase. The shortest stereocilia, which lack side plaques, showed no concentration rise on their sides. Thus, the specific localization of myosin-Iβ at both ends of tip links supports its role as the adaptation motor.
|Original language||English (US)|
|Number of pages||11|
|Journal||Journal of Neuroscience|
|State||Published - Nov 1 1998|
- Electron microscopy
- Hair cell
ASJC Scopus subject areas