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Locatization of Voltaae-sensitive Ca2+ Fluxes and Neuropeptide Y Immunoreactivity to Varicosities in SH-SY5Y Human Neuroblastoma Cells Differentiated by Treatment with the Protein Kinase Inhibitor Staurosporine



The distribution of voltage-sensitive elevations of the level of Ca2+ in untreated SH-SY5Y cells and cells that had been induced to differentiate with staurosporine was investigated by monitoring fura-2 fluorescence in cell suspensions, and by using microfluorometry and quantitative fluorescence imaging on cell bodies and on cellular processes. Cell bodies of both types of cells displayed small Ca2+ elevations, which were composed of transient and sustained components. Elevations were partially sensitive to the L- and N-channel blockers nifedipine (1 μM) and ω-conotoxin GVIA (100 nM) respectively. Up to ten times higher Ca2+ elevations were observed in varicosities of treated cells than in cell bodies of treated and untreated cells. These elevations were insensitive to compounds known to release Ca2+ from intracellular stores. Elevations of Ca2+ were sustained, and they were insensitive to 5 pM nifedipine, 100 nM ω-agatoxin IVA and 100 nM ω-conotoxin GVIA, and partially sensitive to 2 pM ω-conotoxin GVIA, indicating predominance of non-L-type, non-N-type, non-P-type channel activity. The intracellular localization of neuropeptide Y, a marker of differentiation in these cells, was also investigated by fluorescence immunocytochemistry. Varicosities of treated cells displayed marked fluorescence when viewed in a confocal microscope. These findings show that the varicosities of staurosporine-treated cells exhibit some of the functional properties of nerve terminals. The varicosities resemble boutons en passant nerve endings and they seem to express Ca2+ channels different from those in the cell body.