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Residual cone vision without α-transducin

Stockman, A.; Smithson, H.E.; Michaelides, M.; Moore, A.T.; Webster, A.R.; Sharpe, L.T.; (2007) Residual cone vision without α-transducin. Journal of Vision , 7 (5) pp. 1-13. 10.1167/7.4.8. Gold open access

Abstract

Behavioral experiments in humans with a rare genetic mutation that compromises the function of α-transducin (Gα the α-subunit of the G-protein in the primary cone phototransduction cascade) reveal a residual cone response only viable at high light levels and at low temporal frequencies. It has three characteristic properties. First, it limits temporal frequency sensitivity to the equivalent of a simple first order reaction with a time constant of approximately 140 ms. Second, it delays the visual response by an amount that is also consistent with such a reaction. Third, it causes temporal acuity to be linearly related to the logarithm of the amount of bleached pigment. We suggest that these properties are consistent with the residual function depending on a sluggishly generated cone photobleaching product, which we tentatively identify as a cone metarhodopsin. By activating the transduction cascade, this bleaching product mimics the effects of real light and is therefore one of the molecular origins of “background equivalence,” the long-established observation that the aftereffects of photopigment bleaches and the effects of real background lights are equivalent. Alternative explanations for the residual cone response include the possibilities that there is a secondary phototransduction mechanism that bypasses α-transduction, or that the truncated α-transduction that results from the mutation retains some minimal functionality.

Type: Article
Title: Residual cone vision without α-transducin
Open access status: An open access publication
DOI: 10.1167/7.4.8
Publisher version: http://dx.doi.org/10.1167/7.4.8
Language: English
Keywords: Transducin, equivalent background, photopigment bleaching, flicker sensitivity, critical flicker fusion, transduction cascade, dark adaptation
UCL classification: UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > Institute of Ophthalmology
URI: http://discovery.ucl.ac.uk/id/eprint/7477
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