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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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Closure of the pupil in blowfly eyes by bright white light, which causes a low metarhodopsin fraction. a Time course of the transmittance of the pupil in the blowfly eye measured with a bright, broad-band (white) xenon light source after pre-adaptation with red light and an additional 1 min dark adaptation time. The measured signal (data from Stavenga 1980, Fig. 5) was integrated over the complete spectrum. b The metarhodopsin fraction resulting after various periods of illumination (symbols with error bars, from Stavenga 1980, Fig. 5) and the time course of the metarhodopsin fraction in photoequilibrium calculated for sun light (Fig. 1a) filtered by the blowfly pupillary pigment (Fig. 1b), the optical density of which increases during the illumination time as derived from a, reaching a peak value of 1.4 (dotted), 1.8 (grey), and 2.2 (dashed) at maximum pupil closure (see also Fig. 3a)
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Fig4: Closure of the pupil in blowfly eyes by bright white light, which causes a low metarhodopsin fraction. a Time course of the transmittance of the pupil in the blowfly eye measured with a bright, broad-band (white) xenon light source after pre-adaptation with red light and an additional 1 min dark adaptation time. The measured signal (data from Stavenga 1980, Fig. 5) was integrated over the complete spectrum. b The metarhodopsin fraction resulting after various periods of illumination (symbols with error bars, from Stavenga 1980, Fig. 5) and the time course of the metarhodopsin fraction in photoequilibrium calculated for sun light (Fig. 1a) filtered by the blowfly pupillary pigment (Fig. 1b), the optical density of which increases during the illumination time as derived from a, reaching a peak value of 1.4 (dotted), 1.8 (grey), and 2.2 (dashed) at maximum pupil closure (see also Fig. 3a)

Mentions: An experimental demonstration of how the metarhodopsin fraction depends on the density of the pupillary pigment when a blowfly eye is irradiated with white light is presented in Fig. 4 (modified from Stavenga 1980). An eye of a blowfly was dark adapted for 1 min, and then illuminated for 15 s with bright white light from a xenon lamp, the spectrum of which approximates sunlight. The pupil closed within a few seconds (Fig. 4a). This experiment was repeated with illuminations of different durations and subsequently the metarhodopsin fraction was determined by measuring, in the dark-adapted, open-pupil state, the rhabdomere transmittance at the peak of the metarhodopsin spectrum, from which the absorbance due to the metarhodopsin was calculated. The outcome was that the pupil reduced the initial metarhodopsin fraction from about 0.35 to about 0.15 (Fig. 4b, symbols). The time course of the metarhodopsin fraction during the white illumination period closely resembles the time course of the pupil transmittance (Fig. 4a), indicating that the illumination was so bright that photoequilibria were established effectively instantaneously (<1 s).Fig. 4


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)

Closure of the pupil in blowfly eyes by bright white light, which causes a low metarhodopsin fraction. a Time course of the transmittance of the pupil in the blowfly eye measured with a bright, broad-band (white) xenon light source after pre-adaptation with red light and an additional 1 min dark adaptation time. The measured signal (data from Stavenga 1980, Fig. 5) was integrated over the complete spectrum. b The metarhodopsin fraction resulting after various periods of illumination (symbols with error bars, from Stavenga 1980, Fig. 5) and the time course of the metarhodopsin fraction in photoequilibrium calculated for sun light (Fig. 1a) filtered by the blowfly pupillary pigment (Fig. 1b), the optical density of which increases during the illumination time as derived from a, reaching a peak value of 1.4 (dotted), 1.8 (grey), and 2.2 (dashed) at maximum pupil closure (see also Fig. 3a)
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3040812&req=5

Fig4: Closure of the pupil in blowfly eyes by bright white light, which causes a low metarhodopsin fraction. a Time course of the transmittance of the pupil in the blowfly eye measured with a bright, broad-band (white) xenon light source after pre-adaptation with red light and an additional 1 min dark adaptation time. The measured signal (data from Stavenga 1980, Fig. 5) was integrated over the complete spectrum. b The metarhodopsin fraction resulting after various periods of illumination (symbols with error bars, from Stavenga 1980, Fig. 5) and the time course of the metarhodopsin fraction in photoequilibrium calculated for sun light (Fig. 1a) filtered by the blowfly pupillary pigment (Fig. 1b), the optical density of which increases during the illumination time as derived from a, reaching a peak value of 1.4 (dotted), 1.8 (grey), and 2.2 (dashed) at maximum pupil closure (see also Fig. 3a)
Mentions: An experimental demonstration of how the metarhodopsin fraction depends on the density of the pupillary pigment when a blowfly eye is irradiated with white light is presented in Fig. 4 (modified from Stavenga 1980). An eye of a blowfly was dark adapted for 1 min, and then illuminated for 15 s with bright white light from a xenon lamp, the spectrum of which approximates sunlight. The pupil closed within a few seconds (Fig. 4a). This experiment was repeated with illuminations of different durations and subsequently the metarhodopsin fraction was determined by measuring, in the dark-adapted, open-pupil state, the rhabdomere transmittance at the peak of the metarhodopsin spectrum, from which the absorbance due to the metarhodopsin was calculated. The outcome was that the pupil reduced the initial metarhodopsin fraction from about 0.35 to about 0.15 (Fig. 4b, symbols). The time course of the metarhodopsin fraction during the white illumination period closely resembles the time course of the pupil transmittance (Fig. 4a), indicating that the illumination was so bright that photoequilibria were established effectively instantaneously (<1 s).Fig. 4

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