Hypoxia Enhances [3H]Noradrenaline Release Evoked by Nicotinic Receptor Activation from the Human Neuroblastoma SH-SY5Y

Abstract: We have used the human sympathetic neuronal line SH-SY5Y to investigate the effects of hypoxia on noradrenaline (NA) release evoked by either raised [K⁺]_o (100 m M ) or the nicotinic acetylcholine receptor (nAChR) agonist dimethylphenylpiperazinium iodide (DMPP). NA release was monitored by loading cells with [³H]NA and collecting effluent fractions from perfused cells kept in a sealed perifusion chamber. Cells were challenged twice with either stimulus and release was expressed as that evoked by the second challenge as a fraction of that evoked by the first. K⁺-evoked release was unaffected by hypoxia (P o ₂≅ 30–38 mm Hg), but release evoked by DMPP was significantly increased. For both stimuli, replacement of Ca²⁺_o with 1 m M EGTA abolished NA release. K⁺-evoked release was also dramatically reduced in the presence of 200 µ M Cd²⁺ to block voltage-gated Ca²⁺ channels, but DMPP-evoked release was less affected. In hypoxia, DMPP-evoked Cd²⁺-resistant NA release was dramatically increased. Our findings indicate that hypoxia increases NA release evoked from SH-SY5Y cells in response to nAChR activation by increasing Ca²⁺ influx through the nAChR pore, or by activating an unidentified Cd²⁺-resistant Ca²⁺-influx pathway. As acetylcholine is the endogenous transmitter at sympathetic ganglia, these findings may have important implications for sympathetic activity under hypoxic conditions.