Location of release sites and calcium-activated chloride channels relative to calcium channels at the photoreceptor ribbon synapse

A. J. Mercer, K. Rabl, G. E. Riccardi, N. C. Brecha, S. L. Stella, Wallace B Thoreson

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

Vesicle release from photoreceptor ribbon synapses is regulated by L-type Ca2+ channels, which are in turn regulated by Cl- moving through calcium-activated chloride [Cl(Ca)] channels. We assessed the proximity of Ca2+ channels to release sites and Cl(Ca) channels in synaptic terminals of salamander photoreceptors by comparing fast (BAPTA) and slow (EGTA) intracellular Ca2+ buffers. BAPTA did not fully block synaptic release, indicating some release sites are <100 nm from Ca2+ channels. Comparing Cl(Ca) currents with predicted Ca2+ diffusion profiles suggested that Cl(Ca) and Ca2+ channels average a few hundred nanometers apart, but the inability of BAPTA to block Cl(Ca) currents completely suggested some channels are much closer together. Diffuse immunolabeling of terminals with an antibody to the putative Cl(Ca) channel TMEM16A supports the idea that Cl(Ca) channels are dispersed throughout the presynaptic terminal, in contrast with clustering of Ca2+ channels near ribbons. Cl(Ca) currents evoked by intracellular calcium ion concentration ([Ca2+]i) elevation through flash photolysis of DM-nitrophen exhibited EC50 values of 556 and 377 nM with Hill slopes of 1.8 and 2.4 in rods and cones, respectively. These relationships were used to estimate average submembrane [Ca2+]i in photoreceptor terminals. Consistent with control of exocytosis by [Ca2+] nanodomains near Ca2+ channels, average submembrane [Ca 2+]i remained below the vesicle release threshold (∼400 nM) over much of the physiological voltage range for cones. Positioning Ca2+ channels near release sites may improve fidelity in converting voltage changes to synaptic release. A diffuse distribution of Cl(Ca) channels may allow Ca2+ influx at one site to influence relatively distant Ca2+ channels.

Original languageEnglish (US)
Pages (from-to)321-335
Number of pages15
JournalJournal of Neurophysiology
Volume105
Issue number1
DOIs
StatePublished - Jan 1 2011

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Chloride Channels
Calcium Channels
Synapses
Calcium Chloride
Presynaptic Terminals
Urodela
Vertebrate Photoreceptor Cells
Photolysis
Egtazic Acid
Exocytosis
Cluster Analysis
Buffers
Ions
Calcium
Antibodies
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid

ASJC Scopus subject areas

  • Neuroscience(all)
  • Physiology

Cite this

Location of release sites and calcium-activated chloride channels relative to calcium channels at the photoreceptor ribbon synapse. / Mercer, A. J.; Rabl, K.; Riccardi, G. E.; Brecha, N. C.; Stella, S. L.; Thoreson, Wallace B.

In: Journal of Neurophysiology, Vol. 105, No. 1, 01.01.2011, p. 321-335.

Research output: Contribution to journalArticle

Mercer, A. J. ; Rabl, K. ; Riccardi, G. E. ; Brecha, N. C. ; Stella, S. L. ; Thoreson, Wallace B. / Location of release sites and calcium-activated chloride channels relative to calcium channels at the photoreceptor ribbon synapse. In: Journal of Neurophysiology. 2011 ; Vol. 105, No. 1. pp. 321-335.
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