Vesicle depletion and synaptic depression at a mammalian ribbon synapse.
We estimated the size of the readily releasable pool (RRP) of vesicles at a ribbon synapse in the rat retina by making paired voltage-clamp recordings from presynaptic rod bipolar cells (RBCs) and postsynaptic AII amacrine cells in an in vitro retinal slice preparation. The RRP at each active zone was estimated to constitute seven vesicles, in the range of estimated RRP sizes at conventional synapses. During sustained presynaptic Ca(2+) entry, the RRP could be released with a time constant of about 4 ms. This ribbon synapse exhibited pronounced paired-pulse depression (PPD), which was attributable primarily to vesicle depletion. Recovery from PPD was slow (tau approximately 4 s) but could be accelerated by increasing the duration of the depressing stimulus. The small RRP and very high release probability likely contribute to the transient characteristics of neurotransmission at RBC synapses.
Singer
Joshua H
JH
Synaptic Physiology Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA. j-singer@northwestern.edu
Diamond
Jeffrey S
JS
D025042:Amacrine Cells / Q000502:physiology / Q000528:radiation effects; D000818:Animals; D000831:Animals, Newborn; D001581:Benzothiadiazines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology / Q000528:radiation effects; D066298:In Vitro Techniques; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000166:cytology*; D051245:Retinal Bipolar Cells / Q000502:physiology / Q000528:radiation effects; D013569:Synapses / Q000502:physiology* / Q000528:radiation effects; D013572:Synaptic Vesicles / Q000378:metabolism*; D013997:Time Factors
D001581:Benzothiadiazines; C004639:cyclothiazide; D002118:Calcium