Light regulation of Ca2+ in the cone photoreceptor synaptic terminal

Sue Yeon Choi, Skyler Jackman, Wallace B. Thoreson, Richard H. Kramer

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

Retinal cones are depolarized in darkness, keeping voltage-gated Ca 2+ channels open and sustaining exocytosis of synaptic vesicles. Light hyperpolarizes the membrane potential, closing Ca2+ channels and suppressing exocytosis. Here, we quantify the Ca2+ concentration in cone terminals, with Ca2+ indicator dyes. Two-photon ratiometric imaging of fura-2 shows that global Ca2+ averages ∼360 nM in darkness and falls to ∼190 nM in bright light. Depolarizing cones from their light to their dark membrane potential reveals hot spots of Ca2+ that co-label with a fluorescent probe for the synaptic ribbon protein ribeye, consistent with tight localization of Ca2+ channels near ribbons. Measurements with a low-affinity Ca2+ indicator show that the local Ca2+ concentration near the ribbon exceeds 4 μM in darkness. The high level of Ca2+ near the ribbon combined with previous estimates of the Ca2+ sensitivity of release leads to a predicted dark release rate that is much faster than observed, suggesting that the cone synapse operates in a maintained state of synaptic depression in darkness.

Original languageEnglish (US)
Pages (from-to)693-700
Number of pages8
JournalVisual neuroscience
Volume25
Issue number5-6
DOIs
StatePublished - Sep 2008

Keywords

  • Ca
  • Cone
  • Exocytosis
  • Photoreceptor
  • Synaptic transmission

ASJC Scopus subject areas

  • Physiology
  • Sensory Systems

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