Spatial differences in gap junction gating in the lens are a consequence of connexin cleavage

Gap junctions in the vertebrate lens exhibit spatial differences in pH gating: those in the cortical fibre cells close upon tissue acidification while those in the core region do not. It has been speculated that this difference in channel gating is a consequence of the cleavage of the connexins (Cx) that form the gap junction channels. We report the construction of a truncation mutant of ovine Cx50 which mimicks the cleavage in the intact lens. The construct when expressed in Xenopus oocytes results in the formation of functional channels. Comparison with full-length Cx50 revealed a significant reduction in the pH-sensitivity of the truncated form. This is the first evidence linking the non-uniform gating of gap junction channels in the lens with connexin cleavage. It also reveals how fibre cells in the core region remain connected despite the acidic environment caused by elevated lactate levels.