Mechanism of High-Frequency Signaling at a Depressing Ribbon Synapse.
Ribbon synapses mediate continuous release in neurons that have graded voltage responses. While mammalian retinas can signal visual flicker at 80-100 Hz, the time constant, τ, for the refilling of a depleted vesicle release pool at cone photoreceptor ribbons is 0.7-1.1 s. Due to this prolonged depression, the mechanism for encoding high temporal frequencies is unclear. To determine the mechanism of high-frequency signaling, we focused on an "Off" cone bipolar cell type in the ground squirrel, the cb2, whose transient postsynaptic responses recovered following presynaptic depletion with a τ of ∼0.1 s, or 7- to 10-fold faster than the τ for presynaptic pool refilling. The difference in recovery time course is caused by AMPA receptor saturation, where partial refilling of the presynaptic pool is sufficient for a full postsynaptic response. By limiting the dynamic range of the synapse, receptor saturation counteracts ribbon depression to produce rapid recovery and facilitate high-frequency signaling.
Departments of Ophthalmology and Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
Chad P
CP
Grabner
Departments of Ophthalmology and Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
Charles P
CP
Ratliff
Departments of Ophthalmology and Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
Adam C
AC
Light
Departments of Ophthalmology and Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA. Electronic address: s-devries@northwestern.edu.
Steven H
SH
DeVries
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology; D012160:Retina / Q000502:physiology*; D051245:Retinal Bipolar Cells / Q000378:metabolism*; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology
D002118:Calcium