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Nat Neurosci. 2008 May;11(5):565-71. doi: 10.1038/nn.2110. Epub 2008 Apr 20.

Quantal noise from human red cone pigment.

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Solomon H. Snyder Department of Neuroscience, Room 907 Preclinical Teaching Building, 725 North Wolfe Street, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.


The rod pigment, rhodopsin, shows spontaneous isomerization activity. This quantal noise produces a dark light of approximately 0.01 photons s(-1) rod(-1) in human, setting the threshold for rod vision. The spontaneous isomerization activity of human cone pigments has long remained a mystery because the effect of a single isomerized pigment molecule in cones, unlike that in rods, is small and beyond measurement. We have now overcome this problem by expressing human red cone pigment transgenically in mouse rods in order to exploit their large single-photon response, especially after genetic removal of a key negative-feedback regulation. Extrapolating the measured quantal noise of transgenic cone pigment to native human red cones, we obtained a dark rate of approximately 10 false events s(-1) cone(-1), almost 10(3)-fold lower than the overall dark transduction noise previously reported in primate cones. Our measurements provide a rationale for why mammalian red, green and blue cones have comparable sensitivities, unlike their amphibian counterparts.

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