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Development and Function of the Voltage-Gated Sodium Current in Immature Mammalian Cochlear Inner Hair Cells (Sodium Current in Developing IHCs)

Eckrich, Tobias ; Varakina, Ksenya ; Johnson, Stuart L ; Franz, Christoph ; Singer, Wibke ; Kuhn, Stephanie ; Knipper, Marlies ; Holley, Matthew C ; Marcotti, Walter Barnes, Steven (Editor)

2012, Vol.7(9), p.e45732 [Periódico revisado por pares]

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  • Título:
    Development and Function of the Voltage-Gated Sodium Current in Immature Mammalian Cochlear Inner Hair Cells (Sodium Current in Developing IHCs)
  • Autor: Eckrich, Tobias ; Varakina, Ksenya ; Johnson, Stuart L ; Franz, Christoph ; Singer, Wibke ; Kuhn, Stephanie ; Knipper, Marlies ; Holley, Matthew C ; Marcotti, Walter
  • Barnes, Steven (Editor)
  • Assuntos: Research Article ; Biology ; Medicine ; Physics ; Biophysics ; Neuroscience ; Physics ; Biochemistry ; Otolaryngology
  • É parte de: 2012, Vol.7(9), p.e45732
  • Descrição: Inner hair cells (IHCs), the primary sensory receptors of the mammalian cochlea, fire spontaneous Ca 2+ action potentials before the onset of hearing. Although this firing activity is mainly sustained by a depolarizing L-type (Ca V 1.3) Ca 2+ current ( I Ca ), IHCs also transiently express a large Na + current ( I Na ). We aimed to investigate the specific contribution of I Na to the action potentials, the nature of the channels carrying the current and whether the biophysical properties of I Na differ between low- and high-frequency IHCs. We show that I Na is highly temperature-dependent and activates at around −60 mV, close to the action potential threshold. Its size was larger in apical than in basal IHCs and between 5% and 20% should be available at around the resting membrane potential (−55 mV/−60 mV). However, in vivo the availability of I Na could potentially increase to >60% during inhibitory postsynaptic potential activity, which transiently hyperpolarize IHCs down to as far as −70 mV. When IHCs were held at −60 mV and I Na elicited using a simulated action potential as a voltage command, we found that I Na contributed to the subthreshold depolarization and upstroke of an action potential. We also found that I Na is likely to be carried by the TTX-sensitive channel subunits Na V 1.1 and Na V 1.6 in both apical and basal IHCs. The results provide insight into how the biophysical properties of I Na in mammalian cochlear IHCs could contribute to the spontaneous physiological activity during cochlear maturation in vivo .
  • Idioma: Inglês

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