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Mediatophore is a protein that translocates acetyicholine (ACh) on calcium action. It is a homopolymer of a 15-kDa proteolipid that is also a constituent of the membrane sector of vacuolar H + -adenosine trisphosphatase (V-ATPase; vacuolar proton pump). Experiments on neuroblastoma cell lines (N18TG-2) that are deficient for ACh release and on cells that are competent for release, such as the glioma C6BU-1 or the N18TG-2/ C6BU-1 fusion product NG1O8-15, show that there is a correlation between ACh release and the 1 5-kDa proteolipid content of the cell membrane. In another cell line, L-M(TK-), it has been possible to up-regulate ACh release and the membrane proteolipid content after treating the cells with dibutyryl-cyclic AMP or dexamethasone. As mediatophore translocates ACh and as V-ATPase may help vesicular ACh storage, it was interesting to determine the respective role of the two proteins in the observed correlation between release and proteolipid content. After blocking vesicular loading with vesamicol, we did not affect release from these cells, suggesting that the observed correlation may be attributed to mediatophore. The acquisition of an ACh release mechanism would then depend on the process that guides the proteolipid to the plasma membrane of the cell. Key Words: Acetylcholine release-15-kDa proteolipid-Mediatophore-Cell membrane.