Purinergic regulation of sound transduction and auditory neurotransmission

Audiol Neurootol. Jan-Feb 2002;7(1):55-61. doi: 10.1159/000046865.

Abstract

In the cochlea, extracellular ATP influences the endocochlear potential, micromechanics, and neurotransmission via P2 receptors. Evidence for this arises from studies demonstrating widespread expression of ATP-gated ion channels (assembled from P2X receptor subunits) and G protein-coupled receptors (P2Y receptors). P2X2 receptor subunits are localized to the luminal membranes of epithelial cells and hair cells lining scala media. These ion channels provide a shunt pathway for K+ ion egress. Thus, when noise exposure elevates ATP levels in this cochlear compartment, the K+ conductance through P2X receptors reduces the endocochlear potential. ATP-mediated K+ efflux from scala media is complemented by a P2Y receptor G protein-coupled pathway that provides coincident reduction of K+ transport into scala media from the stria vascularis when autocrine or paracrine ATP signalling is invoked. This purinergic signalling likely provides a basis for a reactive homoeostatic regulatory mechanism limiting cochlear sensitivity under stressor conditions. Elevation of ATP in the perilymphatic compartment under such conditions is also likely to invoke purinergic receptor-mediated changes in supporting cell micromechanics, mediated by Ca2+ influx and gating of Ca2+ stores. Independent of these humoral actions, ATP can be classified as a putative auditory neurotransmitter based on the localization of P2X receptors at the spiral ganglion neuron-hair cell synapse, and functional verification of ATP-gated currents in spiral ganglion neurons in situ. Expression of P2X receptors by type II spiral ganglion neurons supports a role for ATP as a transmitter encoding the dynamic state of the cochlear amplifier.

MeSH terms

  • Adenosine Triphosphate / physiology
  • Animals
  • Cochlea / physiology*
  • Hair Cells, Auditory / physiology
  • Hearing / physiology*
  • Humans
  • Neurons, Afferent / physiology
  • Receptors, Purinergic / physiology*
  • Signal Transduction / physiology*
  • Spiral Ganglion / physiology
  • Synaptic Transmission / physiology*

Substances

  • Receptors, Purinergic
  • Adenosine Triphosphate