Spectral Tuning in Salamander Visual Pigments Studied with Dihydroretinal Chromophores

Makino, Clint L.; Groesbeek, M.; Lugtenburg, J.; Baylor, D. A.

doi:10.1016/s0006-3495(99)76953-5

Cited by 41 publications

(52 citation statements)

References 83 publications

(111 reference statements)

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“…A pigment state can be defined by its spectral sensitivity, which is described by a mathematical nomogram whose only free parameter is the λ max (Govardovskii et al, 2000). The spectral sensitivity of a pigment state is conferred upon the photoreceptor to give the cellular action spectrum (e.g., Govardovskii et al, 2000; Hillman et al, 1983; Makino et al, 1999). Electrophysiological measurement of the action spectrum is generally more sensitive, by orders of magnitude, than biochemical measurements of the absorption spectrum (Govardovskii et al, 2000).…”

Section: Resultsmentioning

confidence: 99%

Melanopsin Tristability for Sustained and Broadband Phototransduction

Emanuel

2015

Neuron

113

134

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SUMMARY Mammals rely upon three ocular photoreceptors to sense light: rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs). Rods and cones resolve details in the visual scene. Conversely, ipRGCs integrate over time and space, primarily to support “non-image” vision. The integrative mechanisms of ipRGCs are enigmatic, particularly since these cells use a phototransduction motif that allows invertebrates like Drosophila to parse light with exceptional temporal resolution. Here, we provide evidence for a single mechanism that allows ipRGCs to integrate over both time and wavelength. Light distributes the visual pigment, melanopsin, across three states, two silent and one signaling. Photoequilibration among states maintains pigment availability for sustained signaling, stability of the signaling state permits minutes-long temporal summation, and modest spectral separation of the silent states promotes uniform activation across wavelengths. By broadening the tuning of ipRGCs in both temporal and chromatic domains, melanopsin tristability produces signal integration for physiology and behavior.

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Section: Resultsmentioning

confidence: 99%

Melanopsin Tristability for Sustained and Broadband Phototransduction

Emanuel

2015

Neuron

113

134

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“…For salamander red cone pigment with A2 chromophore, we used λ max = 620 nm (ref. 25). For the polymorphic form of the human red cone pigment used here, λ max = 557 nm with A1 chromophore 26 was adopted.…”

Section: Pigment Absorption Spectrum Templatesmentioning

confidence: 99%

Role of visual pigment properties in rod and cone phototransduction

Kefalov

Marsh-Armstrong

et al. 2003

Nature

119

127

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Retinal rods and cones share a phototransduction pathway involving cyclic GMP 1 . Cones are typically 100 times less photosensitive than rods and their response kinetics are several times faster 2 , but the underlying mechanisms remain largely unknown. Almost all proteins involved in phototransduction have distinct rod and cone variants. Differences in properties between rod and cone pigments have been described, such as a 10-fold shorter lifetime of the meta-II state (active conformation) of cone pigment 3, 4, 5, 6 and its higher rate of spontaneous isomerization 7, 8 , but their contributions to the functional differences between rods and cones remain speculative. We have addressed this question by expressing human or salamander red cone pigment in Xenopus rods, and human rod pigment in Xenopus cones. Here we show that rod and cone pigments when present in the same cell produce light responses with identical amplification and kinetics, thereby ruling out any difference in their signalling properties. However, red cone pigment isomerizes spontaneously 10,000 times more frequently than rod pigment. This high spontaneous activity adapts the native cones even in darkness, making them less sensitive and kinetically faster than rods. Nevertheless, additional factors are probably involved in these differences.Human or salamander red cone pigment, together with green fluorescent protein (GFP) for facilitating screening, was introduced as a transgene into Xenopus under the control of the cytomegalovirus (CMV) promoter. In a wild-type or GFP control Xenopus retina, an antibody to red cone pigment labelled only the outer segments of sporadic red cones. In a frog expressing transgenic red cone pigment, however, immunolabelling included the abundant rod outer segments (Fig. 1a). The concentrated labelling of rod outer segments suggested that the localization signal that targets cone pigment to the outer segment is also recognized by rods. The immunostaining was usually non-uniform across the whole retina, suggesting variable expression of the transgenic pigment among the rods (see below).Outer-segment membrane current was recorded from single principal ('red') rods with a suction pipette. Rods expressing transgenic cone pigment showed no marked changes in their flash responses (Fig. 1b), but their sensitivity was, on average, half that of wild-type or GFP control rods ( Fig. 2a and Table 1). In darkness, these rods also showed considerably higher current noise, which was suppressible by light (Fig. 1c). The photosensitivity of the noise, together with its kinetic characteristics (see below), suggested that it originated in the phototransduction pathway. In other control experiments with transgenic human rod pigment expressed in Xenopus rods, no increase in dark noise was observed (data not shown).The increase in dark noise in rods expressing transgenic red cone pigment suggested that cone pigment was more prone to spontaneous isomerization than rod pigment, and that it was coupled functionally to the rod phototrans...

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“…The switch from A1 to A2 encountered in fishes and amphibians as seasonal or developmental changes (Dartnall et al, 1961;Bridges, 1964;Reuter, 1969;Allen & McFarland, 1973;McFarland & Allen, 1977) has two physiologically relevant effects. First, it red-shifts the wavelength of peak absorption (l max ) of the visual pigment by typically more than 20 nm and broadens the absorbance spectrum (Dartnall & Lythgoe, 1965;Bridges, 1967;Bridges & Yoshikami, 1970; for review see Bridges, 1972; about spectral broadening, see Makino et al, 1999). Even partial A1 r A2 substitution strongly enhances sensitivity to long wavelengths.…”

Section: Introductionmentioning

confidence: 99%

The thermal contribution to photoactivation in A2 visual pigments studied by temperature effects on spectral properties

Ala-Laurila¹,

Albert²,

Saarinen

et al. 2003

Vis Neurosci

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Effects of temperature on the spectral properties of visual pigments were measured in the physiological range (5-28 degrees C) in photoreceptor cells of bullfrog (Rana catesbeiana) and crucian carp (Carassius carassius). Absorbance spectra recorded by microspectrophotometry (MSP) in single cells and sensitivity spectra recorded by electroretinography (ERG) across the isolated retina were combined to yield accurate composite spectra from ca. 400 nm to 800 nm. The four photoreceptor types selected for study allowed three comparisons illuminating the properties of pigments using the dehydroretinal (A2) chromophore: (1) the two members of an A1/A2 pigment pair with the same opsin (porphyropsin vs. rhodopsin in bullfrog "red" rods); (2) two A2 pigments with similar spectra (porphyropsin rods of bullfrog and crucian carp); and (3) two A2 pigments with different spectra (rods vs. long-wavelength-sensitive (L-) cones of crucian carp). Qualitatively, the temperature effects on A2 pigments were similar to those described previously for the A1 pigment of toad "red" rods. Warming caused an increase in relative sensitivities at very long wavelengths but additionally a small shift of lambdamax toward shorter wavelengths. The former effect was used for estimating the minimum energy required for photoactivation (Ea) of the pigment. Bullfrog rod opsin with A2 chromophore had Ea = 44.2 +/- 0.9 kcal/mol, significantly lower (one-tailed P < 0.05) than the value Ea = 46.5 +/- 0.8 kcal/mol for the same opsin coupled to A1. The A2 rod pigment of crucian carp had Ea = 42.3 +/- 0.6 kcal/mol, which is significantly higher (one-tailed P < 0.01) than that of the L-cones in the same retina (Ea = 38.3 +/- 0.4 kcal/mol), whereas the difference compared with the bullfrog A2 rod pigment is not statistically significant (two-tailed P = 0.13). No strict connection between lambdamax and Ea appears to exist among A2 pigments any more than among A1 pigments. Still, the A1 --> A2 chromophore substitution in bullfrog opsin causes three changes correlated as originally hypothesized by Barlow (1957): a red-shift of lambdamax, a decrease in Ea, and an increase in thermal noise.

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Spectral Tuning in Salamander Visual Pigments Studied with Dihydroretinal Chromophores

Cited by 41 publications

References 83 publications

Melanopsin Tristability for Sustained and Broadband Phototransduction

Melanopsin Tristability for Sustained and Broadband Phototransduction

Role of visual pigment properties in rod and cone phototransduction

The thermal contribution to photoactivation in A2 visual pigments studied by temperature effects on spectral properties

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