LOCALIZATION OF VOLTAGE-SENSITIVE CA2-Y IMMUNOREACTIVITY TO VARICOSITIES IN SH-SY5Y HUMAN NEUROBLASTOMA-CELLS DIFFERENTIATED BY TREATMENT WITH THE PROTEIN-KINASE INHIBITOR STAUROSPORINE( FLUXES AND NEUROPEPTIDE)

The distribution of voltage-sensitive elevations of the level of Ca2in untreated SH-SY5Y cells and cells that had been induced to differen tiate with staurosporine was investigated by monitoring fura-2 fluores cence in cell suspensions, and by using microfluorometry and quantitat ive fluorescence imaging on cell bodies and on cellular processes. Cel l 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 mu M) and omega-conotoxin GVIA (100 nM) respectively. Up to ten times hig her Ca2+ elevations were observed in varicosities of treated cells tha n in cell bodies of treated and untreated cells. These elevations were insensitive to compounds known to release Ca2+ from intracellular sto res. Elevations of Ca2+ were sustained, and they were insensitive to 5 mu M nifedipine, 100 nM omega-agatoxin IVA and 100 nM omega-conotoxin GVIA, and partially sensitive to 2 mu M omega-conotoxin GVIA, indicat ing predominance of non-L-type, non-l\l-type, non-P-type channel activ ity. The intracellular localization of neuropeptide Y, a marker of dif ferentiation in these cells, was also investigated by fluorescence imm unocytochemistry. Varicosities of treated cells displayed marked fluor escence when viewed in a confocal microscope. These findings show that the varicosities of staurosporine-treated cells exhibit some of the f unctional properties of nerve terminals, The varicosities resemble bou tons en passant nerve endings and they seem to express Ca2+ channels d ifferent from those in the cell body.