Pore Width Of Disease-Causing Connexin26 Containing Channels

Many point mutations of the gap junction protein connexin26 (Cx26) cause nonsyndromic or syndromic deafness. Some of these mutants form functional channels (Cx26deaf). Most Cx26 in the cochlea exists in heteromeric channels along with connexin30 (Cx30). Using a liposome-based assay of channel activity, we explored (a) the permeability of homomeric hemichannels composed of a Cx26deaf alone and of heteromeric hemichannels composed of both Cx26deaf and wild-type Cx30 (Cx26deaf/Cx30) to sucrose, raffinose, iohexol (NycodenzTM) and diatrizoate (HypaqueTM), and (b) concentration dependence of block of the permeability pathway by alpha-cyclodextrin [1-3]. These studies assess the permeability properties of open channels, and do not report differences in channel gating. None of the channels were permeable to diatrizoate, which is smaller than iohexol but negatively charged; all other compounds are uncharged. Consistent with earlier work, the pores of heteromeric Cx26/Cx30 channels (and most Cx26deaf/Cx30 channels) were more restrictive than either homomeric counterpart, a property shown to correlate with selectivity among signaling molecules [1-5]. In heteromeric channels, the data suggest that Cx26deaf mutations G12R and V95M dramatically narrow the pore relative to Cx26/Cx30, and T8M, V84L and N206S widen it to increasing degrees. G12R, V84L and N206S homomeric channels were less restrictive than homomeric Cx26 channels. T8 and G12 have high probability of being pore lining [6-7]. The other mutation sites are not positioned to directly interact with permeants, so likely exert their effects by other mechanisms. Support: R01NS056509 & R21DC07470. 1. Locke, D. J. Biol. Chem. 279:22883 2. Harris, AL. in: Gap Junctions (ed. R. Werner) p.60, IOS Press 3. Bevans, C. Biophys. J. 68:204a 4. Ayad, WA. J. Biol. Chem. 281:16727 5. Bevans, C. J. Biol. Chem. 273:2808 6. Kwon, TK. J. Gen. Physiol. (in press) 7. Oh, S. J. Physiol. 586:2445