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- Title
Light regulation of Ca2+in the cone photoreceptor synaptic terminal.
- Authors
SUE-YEON CHOI; SKYLER JACKMAN; WALLACE B. THORESON; RICHARD H. KRAMER
- Abstract
AbstractRetinal cones are depolarized in darkness, keeping voltage-gated Ca2+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 ?M 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.
- Subjects
PHOTORECEPTORS; CALCIUM ions; NEURAL transmission; EXOCYTOSIS; PHYSIOLOGICAL effects of light; SYNAPSES
- Publication
Visual Neuroscience, 2008, Vol 25, Issue 5/6, p693
- ISSN
0952-5238
- Publication type
Article
- DOI
10.1017/S0952523808080814