The unitary event amplitude of mouse retinal on-cone bipolar cells

Amy Berntson, W. Rowland Taylor

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Light-evoked synaptic currents were recorded from on-cone bipolar cells in the mouse retina. Fluctuations in the synaptic current observed during maintained light steps were analyzed in order to estimate the amplitude of the underlying unitary event. The maximal synaptic current variance was 5-fold larger than the maximum expected from fluctuations in the number of active postsynaptic channels. Due to uncertainty in the contribution from channel variance, we calculated a range of values for the unitary event amplitude. The observed variance could be accounted for if 30-39 synaptic sites randomly generated unitary events with a waveform identical to the flash-response, and an amplitude of -3.1 to -2.4 pA. The amplitude is consistent with gating about five mGluR6 channels. The shape of the variance-mean relation suggests that in bright light transmitter release approaches zero, while in darkness transmitter release saturates the postsynaptic response. Thus the on-cone bipolar cell synapse is operating over its entire possible range. If it is assumed that the postsynaptic response saturates when one unitary event occurs per integration time, then a lower bound for the unitary event rate is 18 events/s/synaptic site. If the unitary event is generated by a single synaptic vesicle, the results suggest the total vesicle cycling rate available for encoding the on-cone bipolar cell signal is about 540-700 s-1.

Original languageEnglish (US)
Pages (from-to)621-626
Number of pages6
JournalVisual neuroscience
Issue number6
StatePublished - Nov 2003
Externally publishedYes


  • Bipolar cells
  • Light responses
  • Mouse
  • Noise analysis
  • Retina
  • Whole-cell voltage clamp

ASJC Scopus subject areas

  • Physiology
  • Sensory Systems


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