Elevated Intracellular Ca2+ Signals by Oxidative Stress Activate Connexin 43 Hemichannels in Osteocytes

Elevated oxidative stress (OS) during aging leads to bone loss. OS increases intracellular Ca2+ ([Ca2+]i), resulting in cellular damage and death. We show earlier that Cx43 hemichannels open in response to OS, which serves as a protective mechanism for osteocytes. However, the underlying mechanism is unknown. Here, we found that treatment with H2O2 increased [Ca2+]i in osteocytes with [Ca2+]i being primarily derived from an extracellular Ca2+ source. Hemichannel opening induced by OS was inhibited by the depletion of [Ca2+]i with BAPTA-AM, a Ca2+ chelator, suggesting that [Ca2+]i influenced the activity of Cx43 hemichannels. Conversely, blockade of hemichannels had no effect on [Ca2+]i. A biotinylation assay showed that cell surface-expressed Cx43 was increased by OS, which could be inhibited by BAPTA-AM, suggesting that [Ca2+]i is necessary for Cx43 migration to the cell surface in response to OS. Together, these data suggest that increased hemichannel activity induced by OS was likely to be caused by elevated [Ca2+]i through increased Cx43 on the cell surface.