Following tracks of hemichannels

It has been suggested that plasma membrane-bound hemichannels perform physiological and pathophysiological functions per se. Such functions require the presence of hemichannels on the cell surface and their accessibility to the extracellular environment for at least some limited period of time. We have previously shown that hemichannels can be labeled by means of antibodies directed to an external loop domain of connexin (Cx) 43. We now provide evidence that trafficking of hemichannel vesicles can be visualized upon binding of a labeled homophilic peptide corresponding to a region of the first extracellular loop (EL1) of Cx43. In vivo imaging was performed after labeling hemichannels from the extracellular site with a mimetic peptide tagged with a fluorochrome (Alexa-546). Using a Cx43-CFP transfected HeLa cell line for incubation with the mimetic peptide, a significant number of double-labeled vesicles were found inside the cells. This double labeling indicates that a portion of Cx43 within the cell had accessed the cell surface as hemichannels where it bound to the peptide and was subsequently endocytosed. Pulse labeling with the peptide showed a decrease in the number of dual-labeled vesicles over time, indicating degradation and/or concurrent recycling of hemichannel vesicles.