Depolarization redistributes synaptic membrane and creates a gradient of vesicles on the synaptic body at a ribbon synapse.
We used electron tomography of frog saccular hair cells to reconstruct presynaptic ultrastructure at synapses specialized for sustained transmitter release. Synaptic vesicles at inhibited synapses were abundant in the cytoplasm and covered the synaptic body at high density. Continuous maximal stimulation depleted 73% of the vesicles within 800 nm of the synapse, with a concomitant increase in surface area of intracellular cisterns and plasmalemmal infoldings. Docked vesicles were depleted 60%-80% regardless of their distance from the active zone. Vesicles on the synaptic body were depleted primarily in the hemisphere facing the plasmalemma, creating a gradient of vesicles on its surface. We conclude that formation of new synaptic vesicles from cisterns is rate limiting in the vesicle cycle.
Lenzi
David
D
Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA.
Crum
John
J
Ellisman
Mark H
MH
Roberts
William M
WM
D000818:Animals; D048429:Cell Size / Q000187:drug effects / Q000502:physiology; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D004558:Electric Stimulation; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D018069:Hair Cells, Vestibular / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008854:Microscopy, Electron; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D011894:Rana pipiens; D012444:Saccule and Utricle / Q000502:physiology* / Q000648:ultrastructure; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013570:Synaptic Membranes / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013572:Synaptic Vesicles / Q000187:drug effects / Q000502:physiology*