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

1 The roles of both Ca2+ and adenosine 3':5'-cyclic monophosphate (cyclic AMP) in carbachol and K+-stimulated [H-3]-noradrenaline release from SH-SY5Y human neuroblastoma cells were examined. 2 Both carbachol and K+ caused a time- and dose-related stimulation of [H-3]-noradrenaline release. The release event in perfused cells was monophasic. Half-maximum 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 carbachol and K+ caused a time- and dose (measured at 3 min)-related stimulation of cyclic AMP formation with half-maximum stimulation occurring at 5 +/- 1 mu M and 49 +/- 2 mh I respectively. In contrast to its effects 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. However, carbachol-evoked (1 mM) release appeared to be unaffected by Ni2+ pretreatment. 5 These data suggest that in SH-SY5Y cells, elevated cyclic AMP levels are not directly involved in [H-3]-noradrenaline release. In addition, carbachol-stimulated release is largely independent of extracellular Ca2+ possibly implying a role for intracellular stored Ca2+ in the release process.