STUDIES ON THE MECHANISM OF [H-3] NORADRENALINE RELEASE FROM SH-SY5Y CELLS - THE ROLE OF CA2-AMP( AND CYCLIC)

1 The roles of both Ca2+ and adenosine 3':5'-cyclic monophosphate (cyc lic AMP) in carbachol and K+-stimulated [H-3]-noradrenaline release fr om SH-SY5Y human neuroblastoma cells were examined. 2 Both carbachol a nd K+ caused a time- and dose-related stimulation of [H-3]-noradrenali ne release. The release event in perfused cells was monophasic. Half-m aximum stimulation measured in statically incubated (3 min) cells was 38 +/- 4 mu M and 63 +/- 4 mM respectively. K+ (100 mM, added)-evoked release was greater than that produced by carbachol (1 mM). 3 Both car bachol and K+ caused a time- and dose (measured at 3 min)-related stim ulation of cyclic AMP formation with half-maximum stimulation occurrin g at 5 +/- 1 mu M and 49 +/- 2 mh I respectively. In contrast to its e ffects on release, carbachol produced a greater stimulation of cyclic AMP formation than K+.4 K+-stimulated [H-3]-noradrenaline release was entirely dependent on Ca2+ entry as 2.5 mM Ni2+ abolished release. How ever, carbachol-evoked (1 mM) release appeared to be unaffected by Ni2 + pretreatment. 5 These data suggest that in SH-SY5Y cells, elevated c yclic AMP levels are not directly involved in [H-3]-noradrenaline rele ase. In addition, carbachol-stimulated release is largely independent of extracellular Ca2+ possibly implying a role for intracellular store d Ca2+ in the release process.