Two modes of release shape the postsynaptic response at the inner hair cell ribbon synapse.
Two modes of release shape the postsynaptic response at the inner hair cell ribbon synapse.
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DOI：
10.1523/jneurosci.4439-09.2010
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发表时间：
2010-03-24
期刊：
影响因子：
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通讯作者：
Glowatzki E
中科院分区：
文献类型：
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作者：
Grant L;Yi E;Glowatzki E
Cochlear inner hair cells (IHCs) convert sounds into receptor potentials and via their ribbon synapses into firing rates in auditory nerve fibers. Multivesicular release at individual IHC ribbon synapses activates AMPA-mediated excitatory postsynaptic currents (EPSCs) with widely ranging amplitudes. The underlying mechanisms and specific role for multivesicular release in encoding sound are not well understood. Here we characterize the waveforms of individual EPSCs recorded from afferent boutons contacting IHCs and compare their characteristics in immature (postnatal days 8–11) and hearing rats (postnatal days 19–21). Two types of EPSC waveforms were found in every recording: monophasic EPSCs, with sharp rising phases and monoexponential decays, and multiphasic EPSCs, exhibiting inflections on rising and decaying phases. Multiphasic EPSCs exhibited slower rise times and smaller amplitudes than monophasic EPSCs. Both types of EPSCs had comparable charge transfers, suggesting that they were activated by the release of similar numbers of vesicles, which, for multiphasic EPSCs occurred in a less coordinated manner. On average, a higher proportion of larger, monophasic EPSCs was found in hearing compared to immature rats. In addition, EPSCs became significantly faster with age. The developmental increase in size and speed could improve auditory signaling acuity. Multiphasic EPSCs persisted in hearing animals, in some fibers constituting half of the EPSCs. The proportion of mono-versus multiphasic EPSCs varied widely across fibers, resulting in marked heterogeneity of amplitude distributions. We propose that the relative contribution of two modes of multivesicular release, generating mono- and multiphasic EPSCs, may underlie fundamental characteristics of auditory nerve fibers.
