Hypoxic enhancement of evoked noradrenaline release from the human neuroblastoma SH-SY5Y

The effects of chronic hypoxia (2.5% O(2), 24 h) on [3H]noradrenaline ([3H]NA) release evoked from human neuroblastoma SH-SY5Y cells by depolarisation and by activation of muscarinic receptors was investigated. Depolarization of cells with 100 mM K(+) evoked [3H]NA release, and chronic hypoxia enhanced this release significantly. In fluorimetric studies, the K(+)-evoked rises of [Ca(2+)](i) observed in response to 100 mM K(+) were also significantly enhanced. Muscarine-evoked [3H]NA release was also dramatically enhanced by chronic hypoxia. However, muscarine-induced release of Ca(2+) from intracellular stores and subsequent capacitative Ca(2+) entry was unaffected. The protein kinase C inhibitors GF 109 203X and RO-31-8220 did not prevent the enhancement of muscarine-evoked release caused by chronic hypoxia. These findings indicate that chronic hypoxia increases release of [3H]NA from human neuroblastoma SH-SY5Y cells. Enhancement of K(+)-evoked release was attributable to an enhancement of depolarisation-mediated Ca(2+) influx. In contrast, the larger enhancement of muscarine-evoked [3H]NA release was not due to greater release of Ca(2+) from internal stores, nor due to enhanced Ca(2+) influx. Furthermore, it was not attributable to activation of protein kinase C. These findings suggest that enhancement of sympathetic output, known to occur following prolonged hypoxia, may be mediated in part by enhancement of exocytosis.