Submitted on October 8, 2004
Accepted on February 21, 2005
Functional consequences of progressive cone dystrophy-associated mutations in the human cone photoreceptor cyclic nucleotide-gated channel CNGA3 subunit
Chunming Liu1 and Michael D Varnum2*
1 Dept. of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, WA, USA; Program in Neuroscience, Washington State University, Pullman, WA, USA
2 Dept. of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, WA, USA; Program in Neuroscience, Washington State University, Pullman, WA, USA; Center for Integrative Biotechnology, Washington State University, Pullman, WA, USA
* To whom correspondence should be addressed. E-mail: varnum{at}wsu.edu.
Progressive cone dystrophies are a genetically heterogeneous group of disorders characterized by early deterioration of visual acuity and color vision, together with psychophysical and electrophysiological evidence of abnormal cone function and cone degeneration. Recently, three mutations in the gene encoding the CNGA3 subunit of cone photoreceptor cyclic nucleotide-gated (CNG) channels have been linked to progressive cone dystrophy in humans. In order to investigate the functional consequences of these mutations, we expressed mutant human CNGA3 subunits in Xenopus oocytes, alone or together with human CNGB3, and studied these channels using patch-clamp recording. Compared to wild-type channels, homomeric and heteromeric channels containing CNGA3-N471S or -R563H subunits exhibited an increase in apparent affinity for cGMP and an increase in the relative agonist efficacy of cAMP compared to cGMP. In contrast, R277C subunits did not form functional homomeric or heteromeric channels. Cell surface expression levels, determined by confocal microscopy of green fluorescent protein (GFP)-tagged subunits and patch-clamp recording, were significantly reduced for both R563H and R277C but unchanged for N471S. Overall, these results suggest that the plasma membrane localization and gating properties of cone CNG channels are altered by progressive cone dystrophy-associated mutations, providing evidence supporting the pathogenicity of these mutations.
