Connexin 43 hemichannels contribute to the propagation of apoptotic cell death in a rat C6 glioma cell model

Gap junctions (GJs) have been demonstrated to communicate cell death signals from apoptotic to healthy cells, thereby spatially extending apoptosis. Before being incorporated into GJs, hemichannels (hemi-GJs) are normally closed but recent evidence suggests that they can be opened by various messengers and conditions, thereby forming a pore through which molecules can enter or leave the cell potentially leading to cell death. The aim of this study was to determine the contribution of GJs and hemichannels in the communication of apoptosis toward surrounding cells. We induced apoptosis in C6 glioma cells stably transfected with connexin (Cx)43, with cytochrome C(cytC) using in situ electroporation and found that healthy surrounding cells underwent apoptotic transformation. Work with various cell death markers, wild-type (WT) and Cx43-expressing cells, inhibitors of GJs and/or hemichannels, and Cx43 gene silencing showed that GJs contribute to the spread of apoptosis in a zone next to where apoptosis was triggered whereas hemichannels also promoted cell death beyond this area. Buffering cytoplasmic Ca2+ changes inhibited the spread of apoptosis in both cases. We conclude that Cx43 hemichannels, in concert with their GJ counterparts, play a role in communicating cytC-induced apoptotic cell death messages.