A highly Ca2+-sensitive pool of vesicles contributes to linearity at the rod photoreceptor ribbon synapse

Neuron. 2004 May 27;42(4):595-605. doi: 10.1016/s0896-6273(04)00254-5.


Studies of the properties of synaptic transmission have been carried out at only a few synapses. We analyzed exocytosis from rod photoreceptors with a combination of physiological and ultrastructural techniques. As at other ribbon synapses, we found that rods exhibited rapid kinetics of release, and the number of vesicles in the releasable pool is comparable to the number of vesicles tethered at ribbon-style active zones. However, unlike other previously studied neurons, we identified a highly Ca(2+)-sensitive pool of releasable vesicles with a relatively shallow relationship between the rate of exocytosis and [Ca(2+)](i) that is nearly linear over a presumed physiological range of intraterminal [Ca(2+)]. The low-order [Ca(2+)] dependence of release promotes a linear relationship between Ca(2+) entry and exocytosis that permits rods to relay information about small changes in illumination with high fidelity at the first synapse in vision.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Ambystoma
  • Animals
  • Calcium / metabolism
  • Calcium / pharmacology
  • Calcium Signaling / drug effects
  • Calcium Signaling / physiology*
  • Egtazic Acid / analogs & derivatives*
  • Exocytosis / drug effects
  • Exocytosis / physiology
  • In Vitro Techniques
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Microscopy, Electron
  • Presynaptic Terminals / drug effects
  • Presynaptic Terminals / metabolism*
  • Presynaptic Terminals / ultrastructure
  • Retinal Rod Photoreceptor Cells / drug effects
  • Retinal Rod Photoreceptor Cells / metabolism*
  • Retinal Rod Photoreceptor Cells / ultrastructure
  • Synapses / drug effects
  • Synapses / metabolism
  • Synapses / physiology*
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology
  • Synaptic Vesicles / drug effects
  • Synaptic Vesicles / metabolism*
  • Synaptic Vesicles / ultrastructure
  • Vision, Ocular / drug effects
  • Vision, Ocular / physiology*


  • 2-nitrophenyl-EGTA
  • Egtazic Acid
  • Calcium