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A.M. DeRosa, X. Gong, T.W. White; Electrophysiological Properties of Gap Junctions Expressing a Spontaneous Cx50 Mutation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4095.
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Mutations in Cx50 have been reported to cause cataracts and microphthalmia in both humans and mice. The mechanisms for how mutated connexins lead to these phenotypes are not well understood. Using the paired Xenopus oocyte system, we tested the electrophysiological properties of gap junctions expressing a naturally occurring Cx50 mutant protein, Cx50–G22R.
Murine Cx50 mutated at amino acid 22 (glycine to arganine) was subcloned in pCS2+, transcribed in vitro and expressed in paired Xenopus oocytes. Protein expression was confirmed, and quantified by immunoblotting. The paired Xenopus oocyte system was used in conjunction with the dual whole–cell voltage clamp technique to analyze differences in macroscopic junctional conductance (Gj), channel kinetics, and voltage gating sensitivity.
This study, demonstrated that Cx50–G22R subunits alone failed to induce electrical coupling. However, the mixed expression of Cx50–G22R and wild–type Cx50 subunits paired to create heteromeric gap junctions formed functional intercellular channels. These junctions exhibited reduced conductance and altered voltage sensitivity when compared to the channels formed by Cx50 subunits alone. Immunoblotting showed that this phenomenon was not the result of differences in protein expression levels.
Taken together these data define, for the first time, the electrophysiological properties of functional gap junctions formed by the heteromeric combination of Cx50 and Cx50–G22R proteins. Our results indicate that expression of Cx50–G22R channels alone does not provide adequate coupling and may contribute to the cause of cataract associated with this mutation.
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