Institute of Neuroscience Faculty

The frog sacculus is an auditory and seismic detector that is exquisitely sensitive to vibrations at frequencies of 25-75 Hz. Sensitivity to vibrations within a particular frequency band (frequency tuning) is a common feature of auditory systems, and is known to involve a variety of sophisticated mechanical and electrical processes. In many auditory organs, including the frog sacculus, it has been proposed that frequency tuning is accomplished primarily by the electrical properties of the sensory receptors (hair cells) themselves. This type of intrinsic frequency tuning in receptor cells is known as "electrical resonance". We are interested in electrical resonance, synaptic transmission, and related specializations of hair cells because of their importance in auditory processing, and more generally as a model system in which to study the cellular physiology of fast signal processing in the nervous system.

Electrical resonance in hair cells involves an interaction between two or more types of ion channels (voltage-gated calcium channels and one or more classes of potassium channels) and the cell's electrical capacitance. We are currently investigating the biophysical properties of these ion channels to determine the basis for electrical resonance in the frog sacculus, and to test whether electrical resonance is sufficient by itself to account for tuning in this organ. We are particularly interested in the role of calcium as a rapid, short-range intracellular messenger, including how the calcium signal is shaped by the presence of high concentrations of diffusible calcium-binding proteins in the cytoplasm. This calcium signal is important for both electrical resonance and for synaptic transmission.

We are also investigating the physiology and anatomy of the hair cell's synapses onto afferent axons. These synapses are specialized for chemical transmission without action potentials. They closely resemble the "ribbon synapses" of photoreceptors and other cells in the retina. We are particularly interested in understanding how the unique anatomical features of these synapses may contribute to their physiological properties.

• Roberts, W.M.  (2006) Snaring otoferlin's role in deafness.  Cell 127:258-260.
• Rutherford, M.  and W.M. Roberts (2006) Frequency selectivity of synaptic exocytosis in frog saccular hair cells. PNAS (USA ) 103: 2898-2903.
• Lenzi, D., J. Crum, M.H. Ellisman, and W.M. Roberts (2002) Depolarization redistributes synaptic membrane and creates a gradient of vesicles on the synaptic body at a ribbon synapse. Neuron 36:649-659.
• Anson, B.D. and W.M. Roberts (2001) Sodium channel distribution on uninnervated and innervated embryonic skeletal myotubes. J. Neurobiol. 48:42-57.
• Armstrong, C.E. and W.M. Roberts (2001) Rapidly inactivating and non-inactivating calcium-activated potassium currents in frog saccular hair cells. J. Physiol. 536(1):49-65.
• Edmonds, B., R. Reyes, B. Schwaller, and W.M. Roberts (2000) Calretinin modifies presynaptic calcium signaling in frog saccular hair cells. Nat. Neurosci. 3:786-790.
• Lenzi, D., J.W. Runyeon, J. Crum, M.H. Ellisman, and W.M. Roberts (1999) Synaptic vesicle populations in saccular hair cells reconstructed by electron tomography. J. Neurosci. 19:119-132.
• Anson, B.D. and W.M. Roberts (1998) A novel voltage clamp technique for focal measurement of ionic currents from cultured skeletal muscle cells. Biophysical J. 74:2963-2972.
• Armstrong, C.E. and W.M. Roberts (1998) Electrical properties of frog saccular hair cells: distortion by enzymatic dissociation. J. Neurosci. 18:2962-2973.
• Armstrong, C.E. and W.M. Roberts (1997) At least three K+ currents are involved in resonance in frog saccular hair cells. Biophys. J., 70:A346.
• Edmonds, B. and W.M. Roberts (1997) Calretinin is present in a subset of hair cells of the frog sacculus. Biophys. J., 72:A298.
• Lenzi, D. and W.M. Roberts (1996) Modeling of synaptic vesicle capture by the synaptic body in frog saccular hair cells. Soc. Neurosci. Abstr. 22:423.15.
• Armstrong, C.E. and W.M. Roberts (1996) Papain alters the resonant frequency of frog saccular hair cells. Soc. Neurosci. Abstr. 22:347.
• Lenzi, D. and W.M. Roberts (1995) Capacitance measurements of latrotoxin-induced exocytosis in saccular hair cells. Soc. Neurosci. Abstr. 21:164.2
• Lenzi, D. and W.M. Roberts (1994) Calcium signaling in hair cells: multiple roles in a compact cell. Curr. Op. Neurobiol. 4:496-502.
• Parsons, T.D., D. Lenzi, W. Almers and W.M. Roberts (1994) Time-resolved studies of calcium triggered exo- and endocytosis in an isolated presynaptic cell. Neuron 13:875-883.
• Roberts, W.M. (1994) Localization of calcium signals by a mobile calcium buffer in frog saccular hair cells.J.Neurosci.14:3246-3262.
• Lenzi, D. and W.M. Roberts (1994) Electrical resonance of frog saccular hair cells measured in the perforated-patch and whole-cell recording configurations. Sc. Neurosci. Abstr. 20:967
• Roberts, W.M. (1993) Spatial calcium buffering in saccular hair cells. Nature 363:74-76.
• Roberts, W.M., R.A. Jacobs, and A.J. Hudspeth (1991) The hair cell as presynaptic terminal. Ann. NY Acad. Sci. 635:221-233.
• Roberts, W.M., R.A. Jacobs, and A.J. Hudspeth (1990) Co-localization of ion channels involved in frequency selectivity and synaptic transmission at presynaptic active zones of hair cells. J. Neurosci. 10:3664-3684.
• Howard, J., W.M. Roberts and A.J. Hudspeth (1988) Mechanoelectrical transduction by hair cells. Ann. Rev. Biophys. Biophys. Chem. 17:99-124.
• Roberts, W.M., J. Howard and A.J. Hudspeth (1988) Hair cells: transduction, tuning and transmission in the internal ear. Ann. Rev. Cell Biol. 4:63-92.
  

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• Department of Biology
• Department of Psychology
• Department of Human Physiology