Properties of ribbon and non-ribbon release from rod photoreceptors revealed by visualizing individual synaptic vesicles

Minghui Chen, Matthew Van Hook, David Zenisek, Wallace B Thoreson

Research output: Contribution to journalArticle

34 Citations (Scopus)

Abstract

Vesicle release from rod photoreceptors is regulated by Ca 2+ entry through L-type channels located near synaptic ribbons. We characterized sites and kinetics of vesicle release in salamander rods by using total internal reflection fluorescence microscopy to visualize fusion of individual synaptic vesicles. A small number of vesicles were loaded by brief incubation with FM1- 43 or a dextran-conjugated, pH-sensitive form of rhodamine, pHrodo. Labeled organelles matched the diffraction-limited size of fluorescent microspheres and disappeared rapidly during stimulation. Consistent with fusion, depolarization-evoked vesicle disappearance paralleled electrophysiological release kinetics and was blocked by inhibiting Ca 2+ influx. Rods maintained tonic release at resting membrane potentials near those in darkness, causing depletion of membrane-associated vesicles unless Ca 2+ entry was inhibited. This depletion of release sites implies that sustained release may be rate limited by vesicle delivery. During depolarizing stimulation, newly appearing vesicles approached the membrane at ~ 800 nm/s, where they paused for ~ 60 ms before fusion. With fusion, vesicles advanced ~ 18 nm closer to the membrane. Release events were concentrated near ribbons, but lengthy depolarization also triggered release from more distant nonribbon sites. Consistent with greater contributions from non-ribbon sites during lengthier depolarization, damaging the ribbon by fluorophore-assisted laser inactivation (FALI) of Ribeye caused only weak inhibition of exocytotic capacitance increases evoked by 200-ms depolarizing test steps, whereas FALI more strongly inhibited capacitance increases evoked by 25 ms steps. Amplifying release by use of non-ribbon sites when rods are depolarized in darkness may improve detection of decrements in release when they hyperpolarize to light.

Original languageEnglish (US)
Pages (from-to)2071-2086
Number of pages16
JournalJournal of Neuroscience
Volume33
Issue number5
DOIs
StatePublished - Jan 30 2013

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Retinal Rod Photoreceptor Cells
Synaptic Vesicles
Darkness
Membranes
Lasers
Urodela
Rhodamines
Dextrans
Microspheres
Exercise Test
Fluorescence Microscopy
Organelles
Membrane Potentials
Light

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Properties of ribbon and non-ribbon release from rod photoreceptors revealed by visualizing individual synaptic vesicles. / Chen, Minghui; Van Hook, Matthew; Zenisek, David; Thoreson, Wallace B.

In: Journal of Neuroscience, Vol. 33, No. 5, 30.01.2013, p. 2071-2086.

Research output: Contribution to journalArticle

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