Studies on the mechanism of [3H]‐noradrenaline release from SH‐SY5Y cells: the role of Ca2+ and cyclic AMP

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Abstract
1 The roles of both Ca2+ and adenosine 3′:5′-cyclic monophosphate (cyclic AMP) in carbachol and K+-stimulated [3H]-noradrenaline release from SH-SY5Y human neuroblastoma cells were examined. 2 Both carbachol and K+ caused a time- and dose-related stimulation of [3H]-noradrenaline release. The release event in perfused cells was monophasic. Half-maximum stimulation measured in statically incubated (3 min) cells was 38 ±4 μm 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 μm and 49 ± 2 mm respectively. In contrast to its effects on release, carbachol produced a greater stimulation of cyclic AMP formation than K+. 4 K+-stimulated [3H]-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 [3H]-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.

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