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

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 mM) 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 (PO2 approximately 30-38 mm Hg), but release evoked by DMPP was significantly increased. For both stimuli, replacement of Ca2+o with 1 mM EGTA abolished NA release. K+-evoked release was also dramatically reduced in the presence of 200 microM 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.