Mammalian cells require a constant O2 supply to produce adequate energy, and sustained
hypoxia can kill cells. Mammals therefore have evolved sophisticated mechanisms to allow their cells to adapt to
hypoxia. In this study, we investigated the role of TRP channels and the Na+-Ca2+ exchanger (NCX) in mediating
hypoxia-induced [Ca2+]i elevation in a model of the O2-sensing rat
pheochromocytoma (PC12) cell line by using Ca2+ imaging and molecular
biological approaches. Non-selective
cation channels, such as TRPC1, 3 and 6, were found to be functionally expressed in PC12 cells. They mediated Ca2+ entry when cells were exposed to acute
hypoxia (PO2 of 15 mmHg), in addition to Ca2+ entry via VGCCs. Blockage of TRPCs by
2APB and
SKF96365 could significantly reduce
hypoxia-mediated [Ca2+]i elevation.
Suramin and
U73122 attenuated the
hypoxia-induced [Ca2+]i elevation, implying the involvement of the
G-protein and PLC pathways in the hypoxic response. In addition to TRPCs and VGCCs, NCX also contributed to the
hypoxia-induced [Ca2+]i elevation, and blockade of NCX by
KBR7943 could significantly decrease the
hypoxia-induced [Ca2+]i elevation. Our results suggest that the activation of TRP by
hypoxia could lead to NCX reversal; furthermore, membrane depolarization and TRPCs may play a primary role in mediating the hypoxic response in PC12 cells.