We are interested in hair cells and their afferent neurons as models of several kinds of processing by cells of the nervous system. First, they are models of sensory transduction in general and mechanotransduction specifically, more accessible than other mechanosensors such as somatosensory nerve endings. Second, hair cells have provided powerful examples of regulation of ion channel repertoires to create signals – in this case, receptor potentials. For example, hair cells express diverse K+ channels in specific complements in order to produce particular qualities and frequencies of tuning. Third, hair cells are relatively large, accessible presynaptic terminals that release glutamate, like most excitatory synapses in the brain, but which are specialized for unusually high rates of transmission. Finally, hair cells, with their systematically varying morphology and ion channel repertoires, lend themselves well to the study of how cells differentiate during development.
Although we work on diverse hair cell epithelia, our principal model preparation has been the rodent utricular epithelium (Figure 1), which senses linear head movements. Mammalian vestibular epithelia have unusual synaptic diversity: afferent neurons form large cup-shaped synaptic endings (calyces) on type I hair cells, as shown in Figure 2, and more conventional small endings (boutons) on type II hair cells. Details of hair bundle and synaptic morphology, calcium binding protein expression and ion channel properties co-vary as functions of location in the epithelium. We use biophysical and molecular tools to characterize the ion channel properties in both hair cells and afferent neurons. We then use molecular methods to identify the ion channels and modeling to identify the functional significance of distinctive ion channel properties.
