Abstract
Variability in the single photon responses of rod photoreceptors limits the accuracy with which the number and timing of photon absorptions are encoded. We investigated how much single photon responses of mammalian rods fluctuate and what mechanisms control these fluctuations. Mammalian rods, like those of toads, generated responses to single photons with trial-to-trial fluctuations 3-4 times smaller than other familiar signals produced by single molecules. We used the properties of the measured fluctuations to constrain models for how the single photon responses are regulated. Neither feedback control of rhodopsin's activity nor saturation within the transduction cascade were consistent with experiment. The measured responses, however, could be explained by multistep shutoff of rhodopsin or a combination of multistep shutoff and saturation.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Animals
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Calcium / metabolism
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Calcium Signaling / drug effects
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Calcium Signaling / physiology
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Chelating Agents / pharmacology
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Cyclic GMP / metabolism
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Egtazic Acid / analogs & derivatives*
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Egtazic Acid / pharmacology
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Feedback / drug effects
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Feedback / physiology
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Guinea Pigs
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Ion Channels / metabolism
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Macaca fascicularis
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Membrane Potentials / drug effects
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Membrane Potentials / physiology
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Models, Neurological
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Papio
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Phosphoric Diester Hydrolases / metabolism
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Photic Stimulation*
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Photons*
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Retinal Rod Photoreceptor Cells / drug effects
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Retinal Rod Photoreceptor Cells / metabolism*
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Rhodopsin / metabolism*
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Transducin / metabolism
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Vision, Ocular / drug effects
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Vision, Ocular / physiology*
Substances
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Chelating Agents
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Ion Channels
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Egtazic Acid
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Rhodopsin
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Phosphoric Diester Hydrolases
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Transducin
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Cyclic GMP
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1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
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Calcium