Voltage-gated calcium influx modifies cholinergic inhibition of inner hair cells in the immature rat cochlea.

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Voltage-gated calcium influx modifies cholinergic inhibition of inner hair cells in the immature rat cochlea.

J Neurosci. 2018 May 22;:

Authors: Zachary S, Nowak N, Vyas P, Bonanni L, Albert Fuchs P

Abstract
Until postnatal day 12, inner hair cells of the rat cochlea are invested with both afferent and efferent synaptic connections. With the onset of hearing at P12, the efferent synapses disappear, and afferent (ribbon) synapses operate with greater efficiency. This change coincides with increased expression of voltage-gated potassium channels, the loss of calcium-dependent electrogenesis, and the onset of graded receptor potentials driven by sound. The transient efferent synapses include near-membrane postsynaptic cisterns thought to regulate calcium influx through the hair cell's α9α10-nAChR that activates small conductance Ca2+-activated K+ (SK) channels. Serial section electron microscopy of inner hair cells from two 9-day-old (male) rat pups revealed many postsynaptic efferent cisterns and presynaptic afferent ribbons whose average minimal separation in 5 cells ranged from 1.1 to 1.7 μm. Efferent synaptic function was studied in rat pups (7-9 days of age) of either sex. The duration of these SK channel mediated inhibitory synaptic currents (IPSCs) was increased by enhanced calcium influx through L-type voltage-gated channels, combined with ryanodine-sensitive release from internal stores - presumably the near-membrane postsynaptic cistern. These data support the possibility that inner hair cell calcium electrogenesis modulates the efficacy of efferent inhibition during the maturation of inner hair cell synapses.SIGNIFICANCE STATEMENTStrict calcium buffering is essential for cellular function. This problem is especially acute for compact hair cells where increasing cytoplasmic calcium promotes the opposing functions of closely adjoining afferent and efferent synapses. The near-membrane postsynaptic cistern at efferent synapses segregates synaptic calcium signals by acting as a dynamic calcium store. The hair cell serves as an informative model for synapses with postsynaptic cisterns ('C-synapses') found in central neurons.

PMID: 29789373 [PubMed - as supplied by publisher]

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