HYPOXIA ENHANCES [H-3]NORADRENALINE RELEASE EVOKED BY NICOTINIC RECEPTOR ACTIVATION FROM THE HUMAN NEUROBLASTOMA SH-SY5Y

We have used the human sympathetic neuronal line SK-SY5Y to investigat e the effects of hypoxia on noradrenaline (NA) release evoked by eithe r raised [K+](o) (100 mM) or the nicotinic acetylcholine receptor (nAC hR) agonist dimethylphenylpiperazinium iodide (DMPP). NA release was m onitored by loading cells with [H-3] NA and collecting effluent fracti ons from perfused cells kept in a sealed perifusion chamber. Cells wer e challenged twice with either stimulus and release was expressed as t hat evoked by the second challenge as a fraction of that evoked by the first. K+-evoked release was unaffected by hypoxia (PO2 congruent to 30-38 mm Hg), but release evoked by DMPP was significantly increased. For both stimuli, replacement of Ca-o(2+) with 1 mM EGTA abolished NA release. K+-evoked release was also dramatically reduced in the presen ce of 200 mu M Cd2+ to block voltage-gated Ca2+ channels, but DMPP-evo ked release was less affected. In hypoxia, DMPP-evoked Cd2+-resistant NA release was dramatically increased. Our findings indicate that hypo xia increases NA release evoked from SH-SY5Y cells in response to nACh R activation by increasing Ca2+ influx through the nAChR pore, or by a ctivating an unidentified Cd2+-resistant Ca2+-influx pathway. As acety lcholine is the endogenous transmitter at sympathetic ganglia, these f indings may have important implications for sympathetic activity under hypoxic conditions.