We have examined the effects of two intravenous anaesthetic induction agents, propofol and thiopentone, on K+ and carbachol evoked [3H]noradrenaline release from a human neuroblastoma cell line, SH-SY5Y. In this model, we have previously demonstrated that K+ evoked [3H]noradrenaline release was dependent on Ca2+ entry and carbachol evoked release was extracellular Ca(2+)- independent. Propofol inhibited K+ (100 mM)-evoked (IC50 of 42 +/- 11 microM), but not carbachol (1 mM)-evoked, [3H]noradrenaline release. Thiopentone inhibited both K+- and carbachol-evoked release with IC50 values of 116 +/- 15 microM and 169 +/- 39 microM, respectively. These inhibitory effects were not due to changes in the release dynamics, as assessed using perfused cells. Furthermore, thiopentone inhibition of carbachol-evoked release was not due to muscarinic receptor antagonism. Both propofol and thiopentone caused noncompetitive inhibition of K+-stimulated Ca2+ influx, with IC50 values of 127 +/- 7 microM and 121 +/- 10 microM, respectively. These effects were not due to interaction with GABAA receptors, but suggest that both compounds block voltage-sensitive Ca2+ channels. Thiopentone, but not propofol, inhibited carbachol-stimulated increased intracellular Ca2+ concentrations in the presence and absence of extracellular Ca2+. However, thiopentone had no effect on carbachol-stimulated inositol (1,4,5)-triphosphate formation, suggesting that thiopentone may directly inhibit Ca2+ release from intracellular stores.