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M. Cornwall, S. Jin, D.D. Oprian; The Molecular Mechanisms of Congenital Night Blindness . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4162.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Three rhodopsin mutations, G90D, T94I, and A292E, have been found to cause the human retinal disease congenital night blindness (CNB). Two models have been proposed to account for how the mutation G90D causes CNB: one involves constitutive activity of the apoprotein opsin; the other suggests that an increased rate of thermal isomerization of the chromophore in rhodopsin is responsible. We have designed molecular genetic and electrophysiological experiments to determine which of these proposed mechanisms is correct. Methods: Transgenic Xenopus laevis were generated in which the G90D, T94I, and A292E mutants of rhodopsin were expressed in the major rod photoreceptor cells. Solitary rod photoreceptors were isolated from dark-adapted frog retinae and placed in a chamber on the stage of an inverted microscope for electrophysiological recording. Measurements of sensitivity and response kinetics were made in darkness before and after treatment with exogenously applied 11-cis-retinal. Results: Mutant photoreceptor responses displayed accelerated response kinetics (dim flash) and desensitization similar to photoresponses measured from wild-type light adapted rods. The average desensitization compared to wild-type was: G90D: 0.5 log units; T94I: 0.8 log units; and A292E: 1.2 log units. Administration of exogenous 11- cis-retinal (50-250 µM in Ringer) for 5 min resulted in increased sensitivity of mutant responses and slowing of response kinetics to levels that were observed with dark-adapted wild-type rods. Conclusions: Our results are consistent with a model in which constitutively active opsin is the basis for the disease and inconsistent with one based on thermal isomerization.
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