We examined the effects of
hypoxia on the release of
dopamine (DA) and
norepinephrine (NE) from rat
pheochromocytoma 12 (PC-12) cells and assessed the involvement of Ca2+ and
protein kinases in stimulus-secretion coupling.
Catecholamine release was monitored by microvoltammetry using a
carbon fiber electrode as well as by HPLC coupled with electrochemical detection (ECD). Microvoltammetric analysis showed that
hypoxia-induced
catecholamine secretion (PO2 of medium approximately 40 mmHg) occurred within 1 min after the onset of the stimulus and reached a plateau between 10 and 15 min. HPLC-ECD analysis revealed that, at any level of PO2, the release of NE was greater than the release of DA. In contrast, in response to K+ (80 mM), DA release was approximately 11-fold greater than NE release. The magnitude of
hypoxia-induced NE and DA releases depended on the passage, source, and culture conditions of the PC-12 cells. Omission of extracellular Ca2+ or addition of voltage-gated Ca2+ channel blockers attenuated
hypoxia-induced release of both DA and NE to a similar extent.
Protein kinase inhibitors,
staurosporine (200 nM) and
bisindolylmaleimide I (2 microM), on the other hand, attenuated
hypoxia-induced NE release more than DA release. However,
protein kinase inhibitors had no significant effect on K+-induced NE and DA releases. These results demonstrate that
hypoxia releases
catecholamines from PC-12 cells and that, for a given change in PO2, NE release is greater than DA release. It is suggested that
protein kinases are involved in the enhanced release of NE during
hypoxia.