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Metarhodopsin control by arrestin, light-filtering screening pigments, and visual pigment turnover in invertebrate microvillar photoreceptors.

Stavenga DG, Hardie RC - J. Comp. Physiol. A Neuroethol. Sens. Neural. Behav. Physiol. (2010)

Bottom Line: Slow metarhodopsin degradation and rhodopsin regeneration processes further subserve visual pigment maintenance.In most insect eyes, where the majority of photoreceptors have green-absorbing rhodopsins and blue-absorbing metarhodopsins, natural illuminants are predicted to create metarhodopsin levels greater than 60% at high intensities.A simple model for the visual pigment-arrestin cycle is used to illustrate the dependence of the visual pigment population states on light intensity, arrestin levels and pigment turnover.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiophysics, University of Groningen, Groningen, The Netherlands. D.G.Stavenga@rug.nl

ABSTRACT
The visual pigments of most invertebrate photoreceptors have two thermostable photo-interconvertible states, the ground state rhodopsin and photo-activated metarhodopsin, which triggers the phototransduction cascade until it binds arrestin. The ratio of the two states in photoequilibrium is determined by their absorbance spectra and the effective spectral distribution of illumination. Calculations indicate that metarhodopsin levels in fly photoreceptors are maintained below ~35% in normal diurnal environments, due to the combination of a blue-green rhodopsin, an orange-absorbing metarhodopsin and red transparent screening pigments. Slow metarhodopsin degradation and rhodopsin regeneration processes further subserve visual pigment maintenance. In most insect eyes, where the majority of photoreceptors have green-absorbing rhodopsins and blue-absorbing metarhodopsins, natural illuminants are predicted to create metarhodopsin levels greater than 60% at high intensities. However, fast metarhodopsin decay and rhodopsin regeneration also play an important role in controlling metarhodopsin in green receptors, resulting in a high rhodopsin content at low light intensities and a reduced overall visual pigment content in bright light. A simple model for the visual pigment-arrestin cycle is used to illustrate the dependence of the visual pigment population states on light intensity, arrestin levels and pigment turnover.

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a Spectral distribution of the photon flux from natural sources: the sky, the sun and grass. b Absorbance spectra of the pigments in the eye of the blowfly C.vicina. The red screening pigment is located distally in the eye in the screening pigment cells (from Schwemer 1979), and the yellow pupillary pigment is located in the soma of the photoreceptor cells (from Stavenga 2004, Fig. 7). c Absorbance spectra of eye pigments of a few other insects: the screening pigment spectrum of the honey bee Apismellifera (from Strother and Casella 1972, Fig. 8), the pupillary pigment of the wasp Vespa germanica (from Stavenga and Kuiper 1977, Fig. 10), and the screening pigment of a Heliconius butterfly (from Langer and Struwe 1972, Fig. 6)
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Fig1: a Spectral distribution of the photon flux from natural sources: the sky, the sun and grass. b Absorbance spectra of the pigments in the eye of the blowfly C.vicina. The red screening pigment is located distally in the eye in the screening pigment cells (from Schwemer 1979), and the yellow pupillary pigment is located in the soma of the photoreceptor cells (from Stavenga 2004, Fig. 7). c Absorbance spectra of eye pigments of a few other insects: the screening pigment spectrum of the honey bee Apismellifera (from Strother and Casella 1972, Fig. 8), the pupillary pigment of the wasp Vespa germanica (from Stavenga and Kuiper 1977, Fig. 10), and the screening pigment of a Heliconius butterfly (from Langer and Struwe 1972, Fig. 6)

Mentions: Photon flux spectra radiated by the sky, sun, and grass were measured on 5 June 1997 under cloudless, bright light conditions with an InstaspecIII (Oriel Instruments) spectrometer. Figure 1a presents normalized spectra, which are used in the initial analyses that treat the photoequilibria of the visual pigments. The measured spectra were in good agreement with those of McFarland and Munz (1976); see also Menzel (1979, Fig. 1). In the latter experiments, the spectral radiance was measured at midday of a clear sky (in Ithaca, New York) within a cone of 15°, which corresponds to 0.054 std or 177 sqdeg (std is steradian and sqdeg is square degree). The measured radiances had peak values, for sky light at λmax ≈ 455 nm, 5 × 1012 photons cm−2 s−1 nm−1 or Es,max = 300 photons μm−2 s−1 nm−1 sqdeg−1; for light from grass (a meadow), at λmax ≈ 555 nm, Eg,max = 70 photons μm−2 s−1 nm−1 sqdeg−1; for sunlight, radiating light from a small angle, being 32′ = 0.53°, at λmax ≈ 605 nm, the resulting irradiance is Wmax = 8 × 106 photons μm−2 s−1 nm−1.Fig. 1


Metarhodopsin control by arrestin, light-filtering screening pigments, and visual pigment turnover in invertebrate microvillar photoreceptors.

Stavenga DG, Hardie RC - J. Comp. Physiol. A Neuroethol. Sens. Neural. Behav. Physiol. (2010)

a Spectral distribution of the photon flux from natural sources: the sky, the sun and grass. b Absorbance spectra of the pigments in the eye of the blowfly C.vicina. The red screening pigment is located distally in the eye in the screening pigment cells (from Schwemer 1979), and the yellow pupillary pigment is located in the soma of the photoreceptor cells (from Stavenga 2004, Fig. 7). c Absorbance spectra of eye pigments of a few other insects: the screening pigment spectrum of the honey bee Apismellifera (from Strother and Casella 1972, Fig. 8), the pupillary pigment of the wasp Vespa germanica (from Stavenga and Kuiper 1977, Fig. 10), and the screening pigment of a Heliconius butterfly (from Langer and Struwe 1972, Fig. 6)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3040812&req=5

Fig1: a Spectral distribution of the photon flux from natural sources: the sky, the sun and grass. b Absorbance spectra of the pigments in the eye of the blowfly C.vicina. The red screening pigment is located distally in the eye in the screening pigment cells (from Schwemer 1979), and the yellow pupillary pigment is located in the soma of the photoreceptor cells (from Stavenga 2004, Fig. 7). c Absorbance spectra of eye pigments of a few other insects: the screening pigment spectrum of the honey bee Apismellifera (from Strother and Casella 1972, Fig. 8), the pupillary pigment of the wasp Vespa germanica (from Stavenga and Kuiper 1977, Fig. 10), and the screening pigment of a Heliconius butterfly (from Langer and Struwe 1972, Fig. 6)
Mentions: Photon flux spectra radiated by the sky, sun, and grass were measured on 5 June 1997 under cloudless, bright light conditions with an InstaspecIII (Oriel Instruments) spectrometer. Figure 1a presents normalized spectra, which are used in the initial analyses that treat the photoequilibria of the visual pigments. The measured spectra were in good agreement with those of McFarland and Munz (1976); see also Menzel (1979, Fig. 1). In the latter experiments, the spectral radiance was measured at midday of a clear sky (in Ithaca, New York) within a cone of 15°, which corresponds to 0.054 std or 177 sqdeg (std is steradian and sqdeg is square degree). The measured radiances had peak values, for sky light at λmax ≈ 455 nm, 5 × 1012 photons cm−2 s−1 nm−1 or Es,max = 300 photons μm−2 s−1 nm−1 sqdeg−1; for light from grass (a meadow), at λmax ≈ 555 nm, Eg,max = 70 photons μm−2 s−1 nm−1 sqdeg−1; for sunlight, radiating light from a small angle, being 32′ = 0.53°, at λmax ≈ 605 nm, the resulting irradiance is Wmax = 8 × 106 photons μm−2 s−1 nm−1.Fig. 1

Bottom Line: Slow metarhodopsin degradation and rhodopsin regeneration processes further subserve visual pigment maintenance.In most insect eyes, where the majority of photoreceptors have green-absorbing rhodopsins and blue-absorbing metarhodopsins, natural illuminants are predicted to create metarhodopsin levels greater than 60% at high intensities.A simple model for the visual pigment-arrestin cycle is used to illustrate the dependence of the visual pigment population states on light intensity, arrestin levels and pigment turnover.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiophysics, University of Groningen, Groningen, The Netherlands. D.G.Stavenga@rug.nl

ABSTRACT
The visual pigments of most invertebrate photoreceptors have two thermostable photo-interconvertible states, the ground state rhodopsin and photo-activated metarhodopsin, which triggers the phototransduction cascade until it binds arrestin. The ratio of the two states in photoequilibrium is determined by their absorbance spectra and the effective spectral distribution of illumination. Calculations indicate that metarhodopsin levels in fly photoreceptors are maintained below ~35% in normal diurnal environments, due to the combination of a blue-green rhodopsin, an orange-absorbing metarhodopsin and red transparent screening pigments. Slow metarhodopsin degradation and rhodopsin regeneration processes further subserve visual pigment maintenance. In most insect eyes, where the majority of photoreceptors have green-absorbing rhodopsins and blue-absorbing metarhodopsins, natural illuminants are predicted to create metarhodopsin levels greater than 60% at high intensities. However, fast metarhodopsin decay and rhodopsin regeneration also play an important role in controlling metarhodopsin in green receptors, resulting in a high rhodopsin content at low light intensities and a reduced overall visual pigment content in bright light. A simple model for the visual pigment-arrestin cycle is used to illustrate the dependence of the visual pigment population states on light intensity, arrestin levels and pigment turnover.

Show MeSH
Related in: MedlinePlus