Thermal Excitation of the Mechanotransduction Apparatus of Hair Cells

• Published in: Neuron (Cambridge, Mass.) Mass.), 2018-02, Vol.97 (3), p.586-595.e4
• Main Authors: Azimzadeh, Julien B., Fabella, Brian A., Kastan, Nathaniel R., Hudspeth, A.J.
• Format: Article
• Language: English
• Subjects: Animals; Auditory organs; auditory system; Channel gating; Female; Hair; Hair cells; Hair Cells, Auditory - physiology; infrared light; kinocilium; Lasers; Light; Light effects; Male; Mammals; Mechanical stimuli; Mechanotransduction; Mechanotransduction, Cellular; Mitochondria; mitochondrion; Motility; Physical Stimulation; Rana catesbeiana; Saccule; stereocilium; Temperature; ultraviolet light; Ultraviolet radiation; Ultraviolet Rays; vestibular system
• ISSN: 0896-6273; 1097-4199
• DOI: 10.1016/j.neuron.2018.01.013

Although a hair bundle is normally deflected by mechanical stimuli, we found that irradiation of a hair cell from the bullfrog’s sacculus with ultraviolet light causes rapid motion of the hair bundle toward its tall edge. This movement is associated with opening of mechanotransduction channels and disappears when tip links are disrupted. We localized the absorptive element responsible for the motion to the region directly below the hair bundle and measured an action spectrum similar to the absorption spectra of mitochondrial constituents. Temperature measurements revealed heating around the site of absorption; direct heating of the hair bundle confirmed that the response to light is mediated through heat. Although mechanical offsets of the hair bundle revealed that heat softens gating springs, it also acts directly to open transduction channels. This study identifies an unconventional method of hair-cell stimulation and clarifies the previously unexplained sensitivity of auditory organs to thermal stimulation. •Hair cells respond mechanically and electrically to ultraviolet light•These responses involve the opening of mechanotransduction channels•Temperature measurements demonstrate that the responses stem from local heating•Heat both softens gating springs and opens mechanotransduction channels Azimzadeh et al. show that hair cells of the inner ear can be stimulated by light without external or genetic manipulation. Chromophores in mitochondria convert light to heat, which subsequently acts on elements of the hair bundle to stimulate it.