Intracellular calcium stores drive slow non-ribbon vesicle release from rod photoreceptors

Minghui Chen, David Križaj, Wallace B. Thoreson

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

Rods are capable of greater slow release than cones contributing to overall slower release kinetics. Slow release in rods involves Ca2+-induced Ca2+ release (CICR). By impairing release from ribbons, we found that unlike cones where release occurs entirely at ribbon-style active zones, slow release from rods occurs mostly at ectopic, non-ribbon sites. To investigate the role of CICR in ribbon and non-ribbon release from rods, we used total internal reflection fluorescence microscopy as a tool for visualizing terminals of isolated rods loaded with fluorescent Ca2+ indicator dyes and synaptic vesicles loaded with dextran-conjugated pH-sensitive rhodamine. We found that rather than simply facilitating release, activation of CICR by ryanodine triggered release directly in rods, independent of plasma membrane Ca2+ channel activation. Ryanodine-evoked release occurred mostly at non-ribbon sites and release evoked by sustained depolarization at non-ribbon sites was mostly due to CICR. Unlike release at ribbon-style active zones, non-ribbon release did not occur at fixed locations. Fluorescence recovery after photobleaching of endoplasmic reticulum (ER)-tracker dye in rod terminals showed that ER extends continuously from synapse to soma. Release of Ca2+ from terminal ER by lengthy depolarization did not significantly deplete Ca2+ from ER in the perikaryon. Collectively, these results indicate that CICR-triggered release at non-ribbon sites is a major mechanism for maintaining vesicle release from rods and that CICR in terminals may be sustained by diffusion of Ca2+ through ER from other parts of the cell.

Original languageEnglish (US)
Article number20
JournalFrontiers in Cellular Neuroscience
Volume8
Issue numberFEB
DOIs
StatePublished - Feb 3 2014

Keywords

  • Calcium-induced calcium release
  • Exocytosis
  • Retina
  • Ribbon synapse
  • Ryanodine receptors
  • Synaptic vesicle
  • Total internal reflection fluorescence microscopy

ASJC Scopus subject areas

  • Cellular and Molecular Neuroscience

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