Quantitative analysis of synaptic release at the photoreceptor synapse

Gabriel Duncan, Katalin Rabl, Ian Gemp, Ruth Heidelberger, Wallace B. Thoreson

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


Exocytosis from the rod photoreceptor Is stimulated by submicromolar Ca2+ and exhibits an unusually shallow dependence on presynaptic Ca2+. To provide a quantitative description of the photoreceptor Ca2+ sensor for exocytosis, we tested a family of conventional and allosteric computational models describing the final Ca2+-binding steps leading to exocytosis. Simulations were fit to two measures of release, evoked by flash-photolysis of caged Ca2+: exocytotlc capacitance changes from individual rods and postsynaptic currents of second-order neurons. The best simulations supported the occupancy of only two Ca2+ binding sites on the rod Ca2+ sensor rather than the typical four or five. For most models, the on-rates for Ca2+ binding and maximal fusion rate were comparable to those of other neurons. However, the off-rates for Ca2+ unbinding were unexpectedly slow. In addition to contributing to the high-affinity of the photoreceptor Ca2+ sensor, slow Ca 2+ unbinding may support the fusion of vesicles located at a distance from Ca2+ channels. In addition, partial sensor occupancy due to slow unbinding may contribute to the linearization of the first synapse In vision.

Original languageEnglish (US)
Pages (from-to)2102-2110
Number of pages9
JournalBiophysical journal
Issue number10
StatePublished - May 19 2010
Externally publishedYes

ASJC Scopus subject areas

  • Biophysics


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