Neurotransmitter release at ribbon synapses in the retina

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    Abstract

    The synapses of photoreceptors and bipolar cells in the retina are easily identified ultrastructurally by the presence of synaptic ribbons, electron- lense bars perpendicular to the plasma membrane at the active zones, extending about 0.5 μm into the cytoplasm. The neurotransmitter, glutamate, is released continuously (tonically) from these 'ribbon synapses' and the rate of release is modulated in response to graded changes in the membrane potential. This contrasts with action potential-driven bursts of release at conventional synapses. Similar to other synapses, neurotransmitter is released at ribbon synapses by the calcium-dependent exocytosis of synaptic vesicles. Most components of the molecular machinery governing transmitter release are conserved between ribbon and conventional synapses, but a few differences have been identified that may be important determinants of tonic transmitter release. For example, the presynaptic calcium channels of bipolar cells and photoreceptors are different from those elsewhere in the brain. Differences have also been found in the proteins involved in synaptic vesicle recruitment to the active zone and in synaptic vesicle fusion. These differences and others are discussed in terms of their implications for neurotransmitter release from photoreceptors and bipolar cells in the retina.

    Original languageEnglish (US)
    Pages (from-to)442-446
    Number of pages5
    JournalImmunology and Cell Biology
    Volume78
    Issue number4
    DOIs
    StatePublished - Sep 9 2000

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    Keywords

    • Bipolar cell
    • Calcium
    • Photoreceptor
    • Synapse
    • Synaptic ribbon
    • Synaptic vesicle

    ASJC Scopus subject areas

    • Immunology and Allergy
    • Immunology
    • Cell Biology

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