Sangaletti, Rachele et al. (2015) International Worm Meeting "C. elegans touch neurons express plasma membrane innexin channels."

Sangaletti, Rachele, Bianchi, Laura, Dahl, Gerhard

[International Worm Meeting, 2015]

In vertebrate gap junctions mediate intercellular communication by regulating diffusion of ions and small molecules between two neighboring cells. Single gap junction channels are formed by two connexons hemichannels, each one residing in a plasma membrane of opposite cells and consisting of six homo or heteromultimers of connexin proteins. In invertebrates gap junctions are formed by evolutionarly-unrelated proteins called innexins. Although innexins exhibit high structural similarity to connexins, they share molecular homology with another family of proteins in vertebrates, named pannexins. Unlike connexin, pannexins have been shown to form non-junctional membrane channels (pannexons), allowing regulated diffusion of ions and signaling molecules like ATP into the extracellular space. Given, the sequence similarity between innexins and pannexins, it was postulated that innexins may function as unpaired channels. While some evidence exist that this might be the case, no activity of innexins as unpaired channels has been documentated in native C. elegans cells. Pannexins have been also shown to play a crucial role in signaling injury during an inflammation/ischemia episode, but their function and regulation has just begun to be explored.Using a combination of electrophysiological and molecular techniques, we report here that C. elegans touch neurons in situ and in culture express a plasma membrane channel that shares with innexins biophysical and pharmacological features. We show that this channel is activated exclusively by mechanical stimuli, is non-selective and it has a large conductance (1 nS). The channel is also blocked by pannexins/innexins inhibitors and displays voltage-dependent and K+-selective subconductance states. Pannexins are also permeable to fluorescent dyes, thus we performed dye uptake experiments on cultured touch neurons. We report here that C. elegans touch neurons take up Ethidium Bromide through a mechanism that is blocked by pannexins/innexins inhibitors demonstrating that is mediated by innexins . Interestingly, we found that unpaired innexin channels in C. elegans touch neurons mediate cell death induced by chemical ischemia. The identification of innexins that function as plasma membrane channels in genetically tractable model system such as C. elegans, will be the first step towards the development of new tools for furthering our understanding of homologous vertebrate pannexins.