The Rockefeller University - Laboratory of Sensory Neuroscience

Hair Cells of the Inner Ear

Screening for Zebrafish Mutations Affecting
Hearing and Balance

Mutation of the Zebrafish's choroideremia Gene
Causes Hair-Cell Degeneration

Paravalbumin 3, A Potent Ca²⁺ Buffer in Hair Cells

Spontaneous Oscillation by Hair Bundles

Electrical Stimulation of Hair-Bundle Movement

Electron-Microscopic Tomographic Analysis of
the Transduction Element

Radixin in the hair bundle

Dynamical instability and the ear's active process

Sunday, July 20, 2008




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Paravalbumin 3, A Potent Ca²⁺ Buffer in Hair Cells

Ca²⁺ signaling serves distinct purposes in different parts of a hair cell. The Ca²⁺ concentration in stereocilia regulates adaptation and, through rapid transduction-channel reclosure, underlies amplification of mechanical signals. In presynaptic active zones, Ca²⁺ mediates the exocytotic release of afferent neurotransmitter. At efferent synapses, Ca²⁺ activates the K+ channels that dominate the inhibitory postsynaptic potential. A copious supply of diffusible protein buffer isolates the three signals by restricting the spread of free Ca²⁺ and limiting the duration of its action. Using cDNA subtraction and a gene-expression assay based on in situ hybridization, we have detected abundant expression of mRNAs encoding the Ca²⁺ buffer parvalbumin 3 in bullfrog saccular and chicken cochlear hair cells. We have also cloned cDNAs encoding this protein from the corresponding inner-ear libraries and raised antisera against recombinant bullfrog parvalbumin 3. Immunohistochemical labeling indicated that parvalbumin 3 is a prominent Ca2²⁺-binding protein in all hair cells of the bullfrog's sacculus and the chicken's cochlea. Quantitive Western-blot analysis discloses that the concentration of parvalbumin 3 in saccular hair cells is approximately 3 mM. Parvalbumin 3 is therefore a significant mobile Ca²⁺ buffer, and perhaps the dominant buffer, in many types of hair cell. Moreover, parvalbumin 3 provides an early marker for developing hair cells in the frog, chicken, and zebrafish.