Endogenous calcium buffering at photoreceptor synaptic terminals in salamander retina

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Calcium operates by several mechanisms to regulate glutamate release at rod and cone synaptic terminals. In addition to serving as the exocytotic trigger, Ca2+ accelerates replenishment of vesicles in cones and triggers Ca2+-induced Ca2+ release (CICR) in rods. Ca2+ thereby amplifies sustained exocytosis, enabling photoreceptor synapses to encode constant and changing light. A complete picture of the role of Ca2+ in regulating synaptic transmission requires an understanding of the endogenous Ca2+ handling mechanisms at the synapse. We therefore used the "added buffer" approach to measure the endogenous Ca2+ binding ratio (κendo) and extrusion rate constant (γ) in synaptic terminals of photoreceptors in retinal slices from tiger salamander. We found that κendo was similar in both cell types-∼25 and 50 in rods and cones, respectively. Using measurements of the decay time constants of Ca2+ transients, we found that γ was also similar, with values of ∼100 s-1 and 160 s-1 in rods and cones, respectively. The measurements of κendo differ considerably from measurements in retinal bipolar cells, another ribbon-bearing class of retinal neurons, but are comparable to similar measurements at other conventional synapses. The values of γ are slower than at other synapses, suggesting that Ca2+ ions linger longer in photoreceptor terminals, supporting sustained exocytosis, CICR, and Ca2+-dependent ribbon replenishment. The mechanisms of endogenous Ca2+ handling in photoreceptors are thus well-suited for supporting tonic neurotransmission. Similarities between rod and cone Ca2+ handling suggest that neither buffering nor extrusion underlie differences in synaptic transmission kinetics.

Original languageEnglish (US)
Pages (from-to)518-528
Number of pages11
JournalSynapse
Volume68
Issue number11
DOIs
StatePublished - Nov 1 2014

Fingerprint

Urodela
Vertebrate Photoreceptor Cells
Presynaptic Terminals
Retina
Synapses
Calcium
Synaptic Transmission
Exocytosis
Retinal Bipolar Cells
Ambystoma
Retinal Neurons
Glutamic Acid
Buffers
Ions
Light

Keywords

  • Added buffer
  • Calcium buffering
  • Calcium extrusion
  • Photoreceptor
  • Retina
  • Synapse
  • Synaptic ribbon

ASJC Scopus subject areas

  • Cellular and Molecular Neuroscience

Cite this

Endogenous calcium buffering at photoreceptor synaptic terminals in salamander retina. / Van Hook, Matthew; Thoreson, Wallace B.

In: Synapse, Vol. 68, No. 11, 01.11.2014, p. 518-528.

Research output: Contribution to journalArticle

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