Molecular aspects of photoreceptor function

Ebrey, Thomas G.; Honig, Barry

doi:10.1017/s0033583500001785

Cited by 116 publications

(36 citation statements)

References 155 publications

(226 reference statements)

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“…A Ca2+ dependent action potential has also been identified in vertebrate cones (Piccolino & Gerschenfeld, 1978). The ionic mechanism underlying the hyperpolarizing receptor potential in the scallop distal photoreceptor and those in the rod and cone are quite different (see Gorman & McReynolds, 1978;Ebrey & Honig, 1975). Nonetheless, membrane repolarization in both vertebrate and invertebrate photoreceptors appears to have a common mechanism involving a voltage-dependent change in Ca2+ permeability.…”

Section: Discussionmentioning

confidence: 99%

“…Its amplitude and time course provide the information about light intensity and duration for further processing by more centrally located neurons in the nervous system of higher invertebrates and vertebrates. In all systems so far studied, the receptor potential is initiated by a lightdependent change in membrane permeability to one or more ions (see Ebrey & Honig, 1975). There is abundant evidence, however, particularly at high light intensities and during prolonged illumination, that non-light dependent changes in membrane permeability occur which modify the shape of the receptor potential.…”

Section: Introductionmentioning

confidence: 99%

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Contribution of calcium and potassium permeability changes to the off response of scallop hyperpolarizing photoreceptors.

Cornwall¹,

Gorman²

1979

The Journal of Physiology

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SUMMARY1. The membrane response of the distal photoreceptors in the retina of the scallop Pectin irradians to the termination of a bright white light (off response) is shown to be composed of the decay of the hyperpolarizing receptor potential and an action potential with slow kinetics.2. The action potential can be produced in darkness in the absence of external Na+ ions by membrane depolarization.3. The action potential is maintained by replacement of external Ca2+ with Sr2+ or Ba2+, but not by Mg2+. In normal external Ca2+ (9 mM), the action potential is abolished by the addition of the Ca2+ inhibitors, La3+, Co2+, and Mn2+ or the organic Ca2+ antagonist D-600.4. Elevated external Ca2+ concentrations increase the rate of rise and peak amplitude of the action potential as well as the rate of repolarization and after hyperpolarization, but decrease the duration.5. The rate of rise and peak amplitude of the action potential are increased by the K+ antagonists tetraethylammonium (TEA) 4-amino-pyridine (4-AP), Ba2+ and procaine. The antagonists have different effects on subsequent phases of the response, however. External TEA and Ba2+ increase the duration, but decrease the rate of repolarization and abolish the after hyperpolarization, whereas external 4-AP and procaine increase the rate of repolarization, decrease the duration and increase the after hyperpolarization.6. The ratio of the Ca2+ to K+ permeability (PC/0PK) estimated from the constant field equation at the peak of the action potential in different external Ca2+ concentrations is close to 1. 7. The maximum rate of rise and the peak amplitude of the action potential are increased by membrane hyperpolarization and decreased by membrane depolarization. They are decreased by background light intensity relative to their value in the dark.8. In normal ASW the action potential can be identified during the off response as a small overshoot of membrane potential relative to its value in the dark.9. The rate of repolarization of the off response in normal ASW is reduced by agents or conditions which inhibit or reduce Ca2+ permeability changes, e.g. external Co2+ and La2+ or zero external Ca2+.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Contribution of calcium and potassium permeability changes to the off response of scallop hyperpolarizing photoreceptors.

Cornwall¹,

Gorman²

1979

The Journal of Physiology

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“…Visual pigments are a class of proteins found in the membranes of photoreceptor cells (for reviews, see refs. 1 and 2). Their chromophoric unit is 11-cis-retinal covalently bound in the form of a Schiff base to the c-amino group of a lysine.…”

mentioning

confidence: 96%

Photoisomerization, energy storage, and charge separation: A model for light energy transduction in visual pigments and bacteriorhodopsin

Ebrey¹,

Callender²,

Dinur³

et al. 1979

Proc. Natl. Acad. Sci. U.S.A.

279

184

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Visual pigments are a class of proteins found in the membranes of photoreceptor cells (for reviews, see refs. 1 and 2). Their chromophoric unit is 11-cis-retinal covalently bound in the form of a Schiff base to the c-amino group of a lysine. The absorption of a photon by a visual pigment initiates a sequence of biochemical events that eventually lead to the generation of a neural signal by a photoreceptor cell. The identity of the primary photochemical event has been a subject of considerable interest and controversy. It was originally suggested that the primary event was an isomerization of the chromophore from its 1 1-cis to an all-trans conformation (3, 4). The strongest evidence favoring this mechanism was the observation (based on spectral data at low temperature) that an artificial pigment containing a 9-cis chromophore had the same photoproduct as rhodopsin itself. It was quite reasonably concluded that the most plausible common photoproduct formed from the two cis isomers is a trans isomer. A number of picosecond absorption studies of the primary event have raised widespread doubts as to the validity of the original model. It was found (5) that the primary event is complete in less than a few picoseconds at room temperature, and it was argued that this is too short a time for isomerization to occur [although other picosecond studies have reached the opposite conclusion (6)]. More recent evidence has come from the observation that at low temperature the rate of the process is significantly inhibited by deuterium replacement of the exchangeable protons on the pigment (7). Since only one proton on the chromophore is exchangeable, it is unlikely that this would have a measurable effect on the rate of isomerization. The picosecond measurements have generated numerous models (7-11) whose major feature is a photochemical proton transfer followed by a thermal cis-trans isomerization that occurs at a later stage. However, the original evidence upon which the suggestion of a cis-trans isomerization was originally based has never been discredited and, thus, it appears necessary to find a molecular model that is consistent with the entire body of available evidence. The purpose of this paper is to present such a model.There are, in fact, a fairly large number of observations that can be used in the construction and evaluation of alternative models. For example, we have shown, by using simple thermodynamic arguments, that a significant fraction of the photon's energy is "stored" in the primary photoproduct (12). Clearly a mechanism for energy storage must be an important component of any model that is proposed. Another energetic constraint may be derived from psychophysical and electrophysiological measurements of the level of thermal noise in photoreceptor cells. We show below that these observations may be interpreted directly in molecular terms and that they require an unusually high thermal activation energy for the primary event that appears to be inconsistent with many of the models that have been proposed.The ...

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“…In rhodopsin, 11-cis retinal is attached to a specific lysine residue of opsin by a protonated Schiff base linkage (2)(3)(4)(5)(6). The known properties of this chromophore have recently been reviewed (7,8). A more detailed knowledge of the excited state properties of retinal should facilitate the elucidation of its function since its absorption spectrum and mechanism of isomerization depend on the character of its excited electronic states.…”

mentioning

confidence: 99%

Retinal has a highly dipolar vertically excited singlet state: implications for vision.

Mathies¹,

Stryer²

1976

Proc. Natl. Acad. Sci. U.S.A.

277

213

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We have measured the effect of an intense electric field on the absorption spectrum of solutions of all-trans retinal, its unprotonated Schiff base with n-butylamine, and the Cl-salt of this protonated Schiff base. The field-induced change in extinction coefficient as a function of wavelength was analyzed to determine the ground-state dipole moment (), the change in dipole moment on excitation (Z), and the direction of A and AU. These experiments have shown that all three species become highly dipolar upon excitation to the first allowed excited singlet state (1IAA = 15.6,9.9,12 D, respectively). The chromophore in all known vertebrate visual pigments is I1-cis retinal (or dehydroretinal) which is isomerized by light to all-trans retinal (1). In rhodopsin, 11-cis retinal is attached to a specific lysine residue of opsin by a protonated Schiff base linkage (2-6). The known properties of this chromophore have recently been reviewed (7,8). A more detailed knowledge of the excited state properties of retinal should facilitate the elucidation of its function since its absorption spectrum and mechanism of isomerization depend on the character of its excited electronic states. However, relatively few direct measurements have been made on the excited states of retinal because of the difficulty of such experiments.We report here the first determination of the ground and excited state dipole moments of all-trans retinal, its Schiff bases, and 11-cis retinal. This was accomplished by measuring the effect of an intense electric field on the absorption spectrum of solutions of these molecules. The Schiff bases of the all-trans isomer were chosen for this initial study because the interpretation of their electric field spectra is more direct than for those of the 11-cis isomer. The striking finding is that excitation of all-trans retinal and its Schiff bases is accompanied by a large shift in negative charge away from the ionone ring end of the molecule. These observations help to characterize the excited states and isomerization mechanism of retinal. Furthermore, these measurements give insight into the interactions between retinal and opsin during the initial stages of visual excitation.

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Molecular aspects of photoreceptor function

Cited by 116 publications

References 155 publications

Contribution of calcium and potassium permeability changes to the off response of scallop hyperpolarizing photoreceptors.

Contribution of calcium and potassium permeability changes to the off response of scallop hyperpolarizing photoreceptors.

Photoisomerization, energy storage, and charge separation: A model for light energy transduction in visual pigments and bacteriorhodopsin

Retinal has a highly dipolar vertically excited singlet state: implications for vision.

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