title: Distribution of the presynaptic calcium sensors, synaptotagmin I/II and synaptotagmin III, in the goldfish and rodent retinas.
abstract: Synaptic vesicle exocytosis is triggered by rises in calcium up to 100 microM at the site of vesicle fusion. The synaptic vesicle proteins synaptotagmin 1 and 2 (Syt I and Syt II) bind calcium at similarly high concentrations and have been proposed as the calcium sensors for fast neurotransmitter release. However, 1 microM calcium produces tonic transmitter release at photoreceptor and bipolar cell synapses in the goldfish retina, suggesting that these synapses use a higher affinity calcium sensor. Immunofluorescent staining with a panel of Syt I/II antibodies detected Syt I/II in both photoreceptor and bipolar cell terminals of the rodent retina. By contrast, no staining of either photoreceptor or protein kinase C (PKC)-labeled bipolar cell terminals was detected in the goldfish retina with any of the Syt I/II antibodies. The high affinity calcium sensor synaptotagmin 3 (Syt III) was localized to the synaptic layers of both goldfish and rodent retinas; however, while Syt III was associated with PKC-labeled bipolar cell terminals in the goldfish retina, it did not co-localize with PKC in the mouse retina. These results suggest that, unlike in their mammalian counterparts, synaptic vesicle exocytosis in goldfish photoreceptor and bipolar cell terminals utilizes a calcium sensor other than Syt I/II, possibly Syt III.
authors.affiliation: Howard Hughes Medical Institute and Harvard Medical School, Boston, MA, USA.
authors.forename: Amy K
authors.initials: AK
authors.lastname: Berntson
authors.forename: Catherine W
authors.initials: CW
authors.lastname: Morgans
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D005089:Exocytosis; D019084:Fluorescent Antibody Technique, Indirect; D006054:Goldfish; D007395:Interneurons / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D013572:Synaptic Vesicles; D050863:Synaptotagmin I; D050861:Synaptotagmin II; D050857:Synaptotagmins
chemical_list: D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D050863:Synaptotagmin I; D050861:Synaptotagmin II; C494311:Syt1 protein, mouse; C494312:Syt1 protein, rat; C494263:Syt2 protein, mouse; C494264:Syt2 protein, rat; C494289:Syt3 protein, mouse; C494291:Syt3 protein, rat; D050857:Synaptotagmins; D011493:Protein Kinase C; D002118:Calcium