SNARE complex at the ribbon synapses of cochlear hair cells: analysis of synaptic vesicle- and synaptic membrane-associated proteins.
Neurotransmitters are released via exocytosis of synaptic vesicles involving a fusion complex consisting of a set of highly conserved proteins, which form a multiprotein complex resulting in the docking of synaptic vesicles at the site of release. There are three major differences between cochlear hair cell synapses and CNS synapses: (i) hair cells have a specialized structure, the synaptic ribbon, to which synaptic vesicles are attached; (ii) hair cells can maintain high and sustained release of neurotransmitter; and (iii) hair cells lack synaptophysin and synapsin. These differences suggest that an unconventional mechanism of neurotransmitter release may be involved at ribbon synapses. In this study we used different and complementary approaches to determine whether or not ribbon-containing hair cells of the cochlea express any component of the core fusion complex found in conventional synapses. Syntaxin 1, the synaptic membrane synaptosome-associated protein (SNAP)-25 and vesicle-associated membrane protein (VAMP or synaptobrevin) were found to be present in the organ of Corti of both rat and guinea-pig, as shown by reverse transcription polymerase chain reaction and Western blotting. In situ hybridization and immunocytochemistry showed mRNA and protein expression, respectively, in both inner and outer hair cells. Synaptotagmins I and II, generally considered to play major roles in neurotransmitter release at central synapses, were not detected in the organ of Corti.
Safieddine
S
S
Laboratory of Neurochemistry, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA. safieddi@nidcd.nih.gov
Wenthold
R J
RJ
D000818:Animals; D015153:Blotting, Western; D002135:Calcium-Binding Proteins; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000502:physiology; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000737:chemistry* / Q000378:metabolism; D017403:In Situ Hybridization; D008562:Membrane Glycoproteins / Q000032:analysis / Q000235:genetics; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000235:genetics*; D018377:Neurotransmitter Agents / Q000378:metabolism; D020419:Photoreceptor Cells, Vertebrate / Q000737:chemistry; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050600:SNARE Proteins; D013572:Synaptic Vesicles / Q000737:chemistry* / Q000378:metabolism; D050825:Synaptosomal-Associated Protein 25; D050857:Synaptotagmins; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D012333:RNA, Messenger; D050600:SNARE Proteins; C494210:Snap25 protein, rat; C494213:Stx1a protein, rat; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins; D050857:Synaptotagmins