Serotonin organelles of rabbit platelets contain synaptophysin.
Synaptophysin, an integral membrane protein of synaptic vesicles in nerve terminals and a class of small translucent vesicles in neuroendocrine cells, was detected in intact rabbit platelets by immunoblotting, immunofluorescence staining and immuno-electron microscopy. In a highly purified preparation of serotonin organelles isolated from rabbit platelets, synaptophysin was enriched approximately 10-15-fold over platelet homogenate. About 80% of total platelet synaptophysin was present in this purified fraction. The apparent molecular mass (approximately 38 kDa) and the extent of glycosylation of platelet-derived synaptophysin was more similar to the neuronal than to the neuroendocrine form of the protein. Immunofluorescence microscopy revealed that synaptophysin was compartmentalized in intact rabbit platelets and immuno-electron microscopy of subcellular fractions showed that it was localized exclusively to the membrane surface of serotonin organelles. No synaptophysin-like immunoreactivity was detected in platelets from other species such as human, guinea pig and rat. Another integral membrane protein of synaptic vesicles, p65, and a family of synaptic vesicle-associated phosphoproteins, the synapsins, were not detected in platelets of any species tested. These results provide evidence that serotonin organelles from rabbit platelets share a subset of protein components with synaptic vesicles from neurons. Synaptophysin in serotonin organelles from rabbit platelets, as suggested for small synaptic vesicles in neurons, might play a role in the formation of protein channels for the exocytotic release of serotonin.
Bähler
M
M
Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, New York.
Cesura
A M
AM
Fischer
G
G
Kuhn
H
H
Klein
R L
RL
Da Prada
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D000818:Animals; D001792:Blood Platelets / Q000737:chemistry* / Q000648:ultrastructure; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D006031:Glycosylation; D006168:Guinea Pigs; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry*; D008854:Microscopy, Electron; D015388:Organelles / Q000737:chemistry* / Q000648:ultrastructure; D011817:Rabbits; D051381:Rats; D012701:Serotonin / Q000378:metabolism*; D016708:Synaptophysin
D008565:Membrane Proteins; D016708:Synaptophysin; D012701:Serotonin