Endogenous calcium buffers regulate fast exocytosis in the synaptic terminal of retinal bipolar cells.
Calcium-triggered exocytosis at the synapse is suppressed by addition of calcium chelators, but the effects of endogenous Ca(2+) buffers have not been tested. We find that 80% of Ca(2+) binding sites in the synaptic terminal of retinal bipolar cells were associated with mobile molecules that suppressed activation of Ca(2+)-sensitive K(+) channels with an efficiency equivalent to approximately 1.2 mM BAPTA. Removing these buffers caused a 30-fold increase in the number of vesicles released by Ca(2+) tail currents lasting approximately 0.5 ms and a 2-fold increase in the rapidly releasable pool of vesicles (RRP). The effects of BAPTA and EGTA indicate that vesicles comprising the RRP were docked at variable distances from Ca(2+) channels. We propose that endogenous Ca(2+) buffers regulate the size of the RRP by suppressing the release of vesicles toward the periphery of the active zone.
Burrone
Juan
J
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom.
Neves
Guilherme
G
Gomis
Ana
A
Cooke
Anne
A
Lagnado
Leon
L
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004558:Electric Stimulation; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D006054:Goldfish; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors
D015220:Calcium Channels; D002614:Chelating Agents; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium