This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. In the mammalian vestibular labyrinth, hair cells are capable of generating axial deformations in response to variations in transmembrane potential. Our understanding of electromechanical transduction in the hair cells depends on precise knowledge of intracellular structure, and efforts to model hair cell physiology are likewise limited to the fidelity of known intracellular geometry. This collaboration focuses on the ultrastructure of vestibular hair cells. More precisely, we are looking at the subcuticular region (below the cuticular plate), using electron tomography to visualize and analyze rootlet architecture at the junction of the stereocilia bundle and apical region of the cell. Our main interest is the striated organelle (SO), a unique structure located at the apical end of hair cells (auditory and vestibular sensory cells), just below the cuticular plate. It is particularly prominent in mammalian type I vestibular hair cells. The central hypothesis we are investigating with aid from the NCMIR is that striated organelles provide structural and functional connections between the apical and basal parts of the hair cell. The goals of this joint effort are to describe the three-dimensional structure of this particular organelle and to identify its components (or at least, some of the components). Our study should appeal to: 1) sensory physiologists interested in mechanisms of sensory transduction and mechanotransduction, 2) neuroscientists interested in feedback from afferents to the transduction apparatus, 3) protein chemists interested in potential new motor proteins, contractile elements, calcium dynamics, and the molecular architecture of these mechanisms, 4) molecular and cell biologists interested in actin, molecular motors, the cytoskeleton and mitochondria, and 5) microscopists and morphologists interested in a new and elegant structural apparatus.