Expression of the vesicular acetylcholine transporter, proteins involved in exocytosis, and functional calcium signaling in varicosities and soma of a murine septal cell line

The expression and localization of the vesicular acetylcholine transporter in a septal cell line, SN56, were investigated. Immunoprecipitation and imm unoblot analysis of postnuclear supernatants indicated that this cell line expresses reasonable amounts of the transporter. Immunofluorescence and con focal microscopy experiments showed that the vesicular transporter is prese nt in varicosities and also in the cell body of differentiated cells. Varic osities have the potential to be functional sites of transmitter release be cause they responded to depolarization with calcium influx through voltage- gated calcium channels and expressed the synaptic proteins synaptotagmin, S V2, synaptophysin, and a subunit of P/Q calcium channels. In the soma of SN 56 cells, the transporter immunoreactivity was similar to that for synaptot agmin, and it colocalized with synaptophysin, but it did not colocalize wit h SV2. Labeling for SV2 appeared prominently in a defined perinuclear struc ture, whereas the two former proteins were widely distributed in the soma, where several endocytic compartments could be identified with the vital dye FM4-64. These data suggest that distinct synaptic vesicle proteins exist i n different subcellular compartments, and consequently they may follow dist inct pathways in neurites before reaching sites of transmitter storage and release in SN56 cells.