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R.T. Mathias, M. Srinivas, T.W. White, F.J. Martinez-Wittinghan; Chemical Simulation of Cx50 Knockout Lenses: Mefloquine Effects on Junctional Coupling and pH Gating . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4266.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previous studies of lenses from Cx50 knockout (KO) mice suggested that loss of Cx50 caused a reduction in coupling conductance of gap junctions in peripheral differentiating fibers (DF) and eliminated their ability to gate closed in response to a drop in pH. However, these lenses were undersized, had reduced transparency and were generally unhealthy. The antimalarial drug Mefloquine (MFQ), a quinoline-methanol compound, has been shown to be an in vitro blocker of exogenously expressed Cx50 but not Cx46. We therefore used MFQ to obtain a chemically induced equivalent of a Cx50 KO lens, which was otherwise normal, and to study the effects on in vivo coupling. Methods: Gap junctional coupling of fiber cells in whole lenses was determined using impedance techniques; pH gating was evaluated by using a bath solution bubbled with 100% carbon dioxide. Results: When wild type (WT) lenses were exposed for 60 min to 10 uM MFQ, the coupling conductance of DF decreased from 1.0±0.1 to 0.5±0.1 S/cm2 of cell to cell contact. In addition, when MFQ treated WT lenses were exposed to 100% CO2, the pH gating was abolished and the coupling conductance remained at 0.5 S/cm2. In contrast, when WT lenses were exposed to CO2, the DF coupling conductance dropped to values well below 0.2 S/cm2, probably to zero. Lastly, Cx46 for Cx50 knock in (KI) lenses contain no Cx50, and MFQ had no effect on coupling in these lenses. Conclusions: MFQ appears to selectively block Cx50 channels in WT lenses and produce a chemically induced Cx50 KO. Consistent with the results from KO lenses, both Cx50 and Cx46 appear to contribute importantly to the coupling conductance of DF. In WT lenses, the pH gating of Cx50 channels appears to co-operatively close the Cx46 channels of DF. Cx50 channel blockade by MFQ may inhibit the conformational change normally associated with pH gating, and thus eliminate the co-operative effects on Cx46 channels. Whatever the mechanism, the novel conclusion is that gating of Cx50 channels in WT lenses appears to be necessary for gating of Cx46 channels.
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