Victor Govardovskii - Academia.edu (original) (raw)
Papers by Victor Govardovskii
Molecular vision, 2015
To experimentally identify and quantify factors responsible for the lower sensitivity of retinal ... more To experimentally identify and quantify factors responsible for the lower sensitivity of retinal cones compared to rods. Electrical responses of frog rods and fish (Carassius) cones to short flashes of light were recorded using the suction pipette technique. A fast solution changer was used to apply a solution that fixed intracellular Ca2+ concentration at the prestimulus level, thereby disabling Ca2+ feedback, to the outer segment (OS). The results were analyzed with a specially designed mathematical model of phototransduction. The model included all basic processes of activation and quenching of the phototransduction cascade but omitted unnecessary mechanistic details of each step. Judging from the response versus intensity curves, Carassius cones were two to three orders of magnitude less sensitive than frog rods. There was a large scatter in sensitivity among individual cones, with red-sensitive cones being on average approximately two times less sensitive than green-sensitive o...
Neuroscience and Behavioral Physiology, 2014
ABSTRACT Until recently, cAMP has been believed to play an important role in the organization of ... more ABSTRACT Until recently, cAMP has been believed to play an important role in the organization of circadian rhythms in the vertebrate eye but not to be directly involved in controlling the phototransduction cascade in photoreceptors. However, given that cAMP levels in photoreceptor cells vary significantly during the day and that cAMP metabolism in photoreceptor cells may itself be light-dependent, it is logical to suggest that cAMP-dependent protein phosphorylation may be a mechanism for tuning phototransduction processes in accordance with ongoing illumination. The current review addresses contemporary data on the structure of the circadian pacemaker in the retina, the involvement of intraphotoreceptor cAMP in its organization, and the known intracellular targets on which cAMP has or may have regulatory influences. Our recent data indicate that changes in cAMP levels have regulatory influences on the photoreceptor cascade. This action may significantly widen the range of adaptation of photoreceptors to illumination conditions, increasing its sensitivity during the dark part of the day and decreasing its sensitivity in bright light.
Zhurnal evoliutsionnoĭ biokhimii i fiziologii
Investigative Ophthalmology & Visual Science
To derive a mathematical model of TMA+ diffusion across the retina that can be used to estimate t... more To derive a mathematical model of TMA+ diffusion across the retina that can be used to estimate the amplitude and kinetics of the light-evoked increase in subretinal hydration and its effect on the concentration of other ions. All experimental data were obtained in chick retina-pigment epithelium-choroid preparations as described in the accompanying paper. Diffusional properties of the retina were derived from the time course of [TMA+]o in the subretinal space (SRS) after changes in the retinal perfusate. Then, the SRS volume changes underlying the light-induced [TMA+]o response can be derived using a mathematical model of TMA+ diffusion. Complete retinal depth series of light-evoked [TMA+]o responses could be simulated by producing a corresponding expansion of the SRS. Volume changes inferred from the diffusion model were 2.2 to 3.8 times larger and more prolonged than could be derived directly from delta [TMA+]o. The model predicted up to a 20% peak increase in subretinal-space hy...
Investigative Ophthalmology & Visual Science
To assess the effects of systemic hypoxia and hyperoxia on the volume of the subretinal space (SR... more To assess the effects of systemic hypoxia and hyperoxia on the volume of the subretinal space (SRS). The authors measured the concentration of the extracellular space marker tetramethylammonium (TMA+) in the intact cat eye using double-barreled ion-selective microelectrodes. The retina was loaded with TMA+ by a single intravitreal injection. Systemic hypoxia was induced by adding nitrogen to the breathing mixture, and hyperoxia was induced by adding oxygen. Hypoxia produced a slow increase in dark- adapted [TMA+]0, which was prominent in amplitude in the distal portion of the retina, suggesting a shrinkage of the SRS. This effect was essentially proportional to the decrease in arterial oxygen tension (PaO2) below the normoxic level. Dark-adapted (TMA+)0 began to increase at a PaO2 of 60 to 80 mm Hg and was enhanced by 13% to 15% at a PaO2 of 40 mm Hg. Because of its slow onset, the size of the increase also was related to the duration of hypoxia. The light-evoked decrease in (TMA+)0...
Neir̆ofiziologiia = Neurophysiology
Responses of the sensory epithelium of the electrically insulated Lorenzinian ampullae in the Bla... more Responses of the sensory epithelium of the electrically insulated Lorenzinian ampullae in the Black Sea skates (Raja clavata) as well as their spike frequency reactions to electrical stimulation were studied under the current-clamp conditions. The preparations have the input resistance of 200-800 k omega, the transepithelial resting potential of 0 divided by -2 mV and ordinary impulse activity in afferent fibres. Electroreceptor thresholds were of 2-10 microV (current approximately 10-11 A). With adequate parameters of stimulation (current up to 1 nA, voltage drop across the epithelium to +/-500 microV) the current-voltage relation of the epithelium was linear without any signs of both spike and oscillatory activity of the receptor cells. With negative currents more than 1-10 nA there appeared a regenerative spike in the epithelium. The spike was accompanied by abnormal impulse in an afferent fibre.
Neir̆ofiziologiia = Neurophysiology
Action of TEA, 4-AP, Co2+, Cd2+, Cs+, EDTA and verapamile on sensory epithelium of Lorenzinian am... more Action of TEA, 4-AP, Co2+, Cd2+, Cs+, EDTA and verapamile on sensory epithelium of Lorenzinian ampullae was studied in the Black Sea skate Raja clavata. Application of TEA to the basal face of epithelium in current-clamped ampulla caused oscillations of transepithelial potential and oscillatory spike discharges in response to excitatory stimulation. The oscillations were suppressed by Co2+, Cd2+ and EDTA. Application of Cs+ was followed by partial or complete suppression of spike response adaptation. TEA injection into the ampulla produced an increase in the spike frequency reaction and speeding of adaptation. Co2+, Cd2+ and verapamile inside the ampulla caused almost no changes. The contribution of various ionic channels to the function of the electroreceptor cell is discussed.
Neir̆ofiziologiia = Neurophysiology
Responses of electrically insulated Lorentzinian ampullae to d. c. pulses were studied on skates ... more Responses of electrically insulated Lorentzinian ampullae to d. c. pulses were studied on skates Raja clavata in the course of polarization of receptor epithelium. With negative polarization of -4 divided by -6 mV reversed changes in spike frequency (acceleration to anodal and inhibition to cathodal pulses) appeared practically without loss of sensitivity, the course of adaptation being unchanged. The data are in accordance with the model described previously suggesting stationary N-shaped voltage-current relation of receptor cell apical membrane.
Tsitologiia
A design of the recording microspectrophotometer is described. The instrument possesses an absolu... more A design of the recording microspectrophotometer is described. The instrument possesses an absolutely flat base line and quantum-noise limited detection threshold. Two principal elements of the design are the "jumping" stage, and the logarithmic amplifier with the phase-sensitive detector which converts the photomultiplier output into the optical density signal. The performance of the instrument is illustrated by the recordings of visual pigment spectra in single photoreceptors.
The Journal of General Physiology
![Research paper thumbnail of [Light-induced calcium ion release from retinal cones]](https://attachments.academia-assets.com/39132785/thumbnails/1.jpg)
](Doklady Akademii nauk SSSR
Rossiĭskii fiziologicheskiĭ zhurnal imeni I.M. Sechenova / Rossiĭskaia akademiia nauk
Visual cycle is the series of reactions that support regeneration of the visual pigmen after its ... more Visual cycle is the series of reactions that support regeneration of the visual pigmen after its photolysis in retinal rods and cones. Inherited or acquired deficiencies of the visual cycle impair dark adaptation and lead to a series of visual disorders. The paper describes a new approach to study of the visual cycle that uses fast dichroic microspectrophotometer. The method allows studying interconversion of bleaching products in single intact photoreceptors in condition approaching the situation in vivo. Using this approach, we established a complete scheme of transitions between metarhodopsins, retinal and retinol in amphibian rods. It appeared that the decay of metarhodopsins controls both the time course of rod dark adaptation following small bleaches and the production of retinol that is the substrate for rhodopsin regeneration. We also obtained novel data on kinetics of the decay of cone metapigments that was found to be by an order of magnitude faster than in rods. Possible ...
Neir̆ofiziologiia = Neurophysiology
In acute experiments on Black Sea skates Raja clavata the potential difference across the sensory... more In acute experiments on Black Sea skates Raja clavata the potential difference across the sensory epithelium and across the skin as well as the impulse activity of single electro-receptors were studied during thermal stimulation of pores of the ampullae of Lorenzini. Heating of the skin near the pore caused a positive potential shift inside the ampullary canal and across the skin (outside with respect to inside) and inhibition of the impulse activity. Cooling of the skin resulted in the opposite effects. Biological significance of the skin mechanism of thermal sensitivity of the ampullae of Lorenzini is discussed.
Doklady Akademii nauk SSSR
Fiziologicheskiĭ zhurnal SSSR imeni I. M. Sechenova
The Journal of General Physiology
Vertebrate rod photoreceptors adjust their sensitivity as they adapt during exposure to steady li... more Vertebrate rod photoreceptors adjust their sensitivity as they adapt during exposure to steady light. Light adaptation prevents the rod from saturating and significantly extends its dynamic range. We examined the time course of the onset of light adaptation in bullfrog rods and compared it with the projected onset of feedback reactions thought to underlie light adaptation on the molecular level. We found that adaptation developed in two distinct temporal phases: (1) a fast phase that operated within seconds after the onset of illumination, which is consistent with most previous reports of a 1-2-s time constant for the onset of adaptation; and (2) a slow phase that engaged over tens of seconds of continuous illumination. The fast phase desensitized the rods as much as 80-fold, and was observed at every light intensity tested. The slow phase was observed only at light intensities that suppressed more than half of the dark current. It provided an additional sensitivity loss of up to 40...
Investigative ophthalmology & visual science
Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology, 2014
Amphibian “green” rods express a blue-sensitive cone visual pigment, and should look yellow. Howe... more Amphibian “green” rods express a blue-sensitive cone visual pigment, and should look yellow. However,when observing them axially under microscope one sees them as green. We used single-cell microspectrophotometry (MSP) to reveal the basis of the perceived color of these photoreceptors. Conventional side-on MSP recording of the proximal cell segments reveals no selective longwave absorbing pigment explaining the green color. End-on MSP recording shows, in addition to the green rod visual pigment, an extra 2- to 4-fold attenuation being almost flat throughout the visible spectrum. This attenuation is absent in red (rhodopsin) rods, and vanishes in green rods when the retina is bathed in high-refractive media, and at wide illumination aperture. The same treatments change the color from green to yellow. It seems that the non-visual pigment attenuation is a result of slender green rod myoids operating as non-selective light guides. We hypothesize that narrow myoids, combined with photome...
Molecular vision, 2009
In a series of works between 1972 and 1984, it was established that rhodopsin undergoes rotationa... more In a series of works between 1972 and 1984, it was established that rhodopsin undergoes rotational and lateral Brownian motion in the plane of photoreceptor membrane. The concept of free movement of proteins of phototransduction cascade is an essential principle of the present scheme of vertebrate phototransduction. This has recently been challenged by findings that show that in certain conditions rhodopsin in the membrane may be dimeric and form extended areas of paracrystalline organization. Such organization seems incompatible with earlier data on free rhodopsin diffusion. Thus we decided to reinvestigate lateral diffusion of rhodopsin and products of its photolysis in photoreceptor membrane specifically looking for indications of possible oligomeric organization. Diffusion exchange by rhodopsin and its photoproducts between bleached and unbleached halves of rod outer segment was traced using high-speed dichroic microspectrophotometer. Measurements were conducted on amphibian (fr...
Molecular vision, 2015
To experimentally identify and quantify factors responsible for the lower sensitivity of retinal ... more To experimentally identify and quantify factors responsible for the lower sensitivity of retinal cones compared to rods. Electrical responses of frog rods and fish (Carassius) cones to short flashes of light were recorded using the suction pipette technique. A fast solution changer was used to apply a solution that fixed intracellular Ca2+ concentration at the prestimulus level, thereby disabling Ca2+ feedback, to the outer segment (OS). The results were analyzed with a specially designed mathematical model of phototransduction. The model included all basic processes of activation and quenching of the phototransduction cascade but omitted unnecessary mechanistic details of each step. Judging from the response versus intensity curves, Carassius cones were two to three orders of magnitude less sensitive than frog rods. There was a large scatter in sensitivity among individual cones, with red-sensitive cones being on average approximately two times less sensitive than green-sensitive o...
Neuroscience and Behavioral Physiology, 2014
ABSTRACT Until recently, cAMP has been believed to play an important role in the organization of ... more ABSTRACT Until recently, cAMP has been believed to play an important role in the organization of circadian rhythms in the vertebrate eye but not to be directly involved in controlling the phototransduction cascade in photoreceptors. However, given that cAMP levels in photoreceptor cells vary significantly during the day and that cAMP metabolism in photoreceptor cells may itself be light-dependent, it is logical to suggest that cAMP-dependent protein phosphorylation may be a mechanism for tuning phototransduction processes in accordance with ongoing illumination. The current review addresses contemporary data on the structure of the circadian pacemaker in the retina, the involvement of intraphotoreceptor cAMP in its organization, and the known intracellular targets on which cAMP has or may have regulatory influences. Our recent data indicate that changes in cAMP levels have regulatory influences on the photoreceptor cascade. This action may significantly widen the range of adaptation of photoreceptors to illumination conditions, increasing its sensitivity during the dark part of the day and decreasing its sensitivity in bright light.
Zhurnal evoliutsionnoĭ biokhimii i fiziologii
Investigative Ophthalmology & Visual Science
To derive a mathematical model of TMA+ diffusion across the retina that can be used to estimate t... more To derive a mathematical model of TMA+ diffusion across the retina that can be used to estimate the amplitude and kinetics of the light-evoked increase in subretinal hydration and its effect on the concentration of other ions. All experimental data were obtained in chick retina-pigment epithelium-choroid preparations as described in the accompanying paper. Diffusional properties of the retina were derived from the time course of [TMA+]o in the subretinal space (SRS) after changes in the retinal perfusate. Then, the SRS volume changes underlying the light-induced [TMA+]o response can be derived using a mathematical model of TMA+ diffusion. Complete retinal depth series of light-evoked [TMA+]o responses could be simulated by producing a corresponding expansion of the SRS. Volume changes inferred from the diffusion model were 2.2 to 3.8 times larger and more prolonged than could be derived directly from delta [TMA+]o. The model predicted up to a 20% peak increase in subretinal-space hy...
Investigative Ophthalmology & Visual Science
To assess the effects of systemic hypoxia and hyperoxia on the volume of the subretinal space (SR... more To assess the effects of systemic hypoxia and hyperoxia on the volume of the subretinal space (SRS). The authors measured the concentration of the extracellular space marker tetramethylammonium (TMA+) in the intact cat eye using double-barreled ion-selective microelectrodes. The retina was loaded with TMA+ by a single intravitreal injection. Systemic hypoxia was induced by adding nitrogen to the breathing mixture, and hyperoxia was induced by adding oxygen. Hypoxia produced a slow increase in dark- adapted [TMA+]0, which was prominent in amplitude in the distal portion of the retina, suggesting a shrinkage of the SRS. This effect was essentially proportional to the decrease in arterial oxygen tension (PaO2) below the normoxic level. Dark-adapted (TMA+)0 began to increase at a PaO2 of 60 to 80 mm Hg and was enhanced by 13% to 15% at a PaO2 of 40 mm Hg. Because of its slow onset, the size of the increase also was related to the duration of hypoxia. The light-evoked decrease in (TMA+)0...
Neir̆ofiziologiia = Neurophysiology
Responses of the sensory epithelium of the electrically insulated Lorenzinian ampullae in the Bla... more Responses of the sensory epithelium of the electrically insulated Lorenzinian ampullae in the Black Sea skates (Raja clavata) as well as their spike frequency reactions to electrical stimulation were studied under the current-clamp conditions. The preparations have the input resistance of 200-800 k omega, the transepithelial resting potential of 0 divided by -2 mV and ordinary impulse activity in afferent fibres. Electroreceptor thresholds were of 2-10 microV (current approximately 10-11 A). With adequate parameters of stimulation (current up to 1 nA, voltage drop across the epithelium to +/-500 microV) the current-voltage relation of the epithelium was linear without any signs of both spike and oscillatory activity of the receptor cells. With negative currents more than 1-10 nA there appeared a regenerative spike in the epithelium. The spike was accompanied by abnormal impulse in an afferent fibre.
Neir̆ofiziologiia = Neurophysiology
Action of TEA, 4-AP, Co2+, Cd2+, Cs+, EDTA and verapamile on sensory epithelium of Lorenzinian am... more Action of TEA, 4-AP, Co2+, Cd2+, Cs+, EDTA and verapamile on sensory epithelium of Lorenzinian ampullae was studied in the Black Sea skate Raja clavata. Application of TEA to the basal face of epithelium in current-clamped ampulla caused oscillations of transepithelial potential and oscillatory spike discharges in response to excitatory stimulation. The oscillations were suppressed by Co2+, Cd2+ and EDTA. Application of Cs+ was followed by partial or complete suppression of spike response adaptation. TEA injection into the ampulla produced an increase in the spike frequency reaction and speeding of adaptation. Co2+, Cd2+ and verapamile inside the ampulla caused almost no changes. The contribution of various ionic channels to the function of the electroreceptor cell is discussed.
Neir̆ofiziologiia = Neurophysiology
Responses of electrically insulated Lorentzinian ampullae to d. c. pulses were studied on skates ... more Responses of electrically insulated Lorentzinian ampullae to d. c. pulses were studied on skates Raja clavata in the course of polarization of receptor epithelium. With negative polarization of -4 divided by -6 mV reversed changes in spike frequency (acceleration to anodal and inhibition to cathodal pulses) appeared practically without loss of sensitivity, the course of adaptation being unchanged. The data are in accordance with the model described previously suggesting stationary N-shaped voltage-current relation of receptor cell apical membrane.
Tsitologiia
A design of the recording microspectrophotometer is described. The instrument possesses an absolu... more A design of the recording microspectrophotometer is described. The instrument possesses an absolutely flat base line and quantum-noise limited detection threshold. Two principal elements of the design are the "jumping" stage, and the logarithmic amplifier with the phase-sensitive detector which converts the photomultiplier output into the optical density signal. The performance of the instrument is illustrated by the recordings of visual pigment spectra in single photoreceptors.
The Journal of General Physiology
Doklady Akademii nauk SSSR
Rossiĭskii fiziologicheskiĭ zhurnal imeni I.M. Sechenova / Rossiĭskaia akademiia nauk
Visual cycle is the series of reactions that support regeneration of the visual pigmen after its ... more Visual cycle is the series of reactions that support regeneration of the visual pigmen after its photolysis in retinal rods and cones. Inherited or acquired deficiencies of the visual cycle impair dark adaptation and lead to a series of visual disorders. The paper describes a new approach to study of the visual cycle that uses fast dichroic microspectrophotometer. The method allows studying interconversion of bleaching products in single intact photoreceptors in condition approaching the situation in vivo. Using this approach, we established a complete scheme of transitions between metarhodopsins, retinal and retinol in amphibian rods. It appeared that the decay of metarhodopsins controls both the time course of rod dark adaptation following small bleaches and the production of retinol that is the substrate for rhodopsin regeneration. We also obtained novel data on kinetics of the decay of cone metapigments that was found to be by an order of magnitude faster than in rods. Possible ...
Neir̆ofiziologiia = Neurophysiology
In acute experiments on Black Sea skates Raja clavata the potential difference across the sensory... more In acute experiments on Black Sea skates Raja clavata the potential difference across the sensory epithelium and across the skin as well as the impulse activity of single electro-receptors were studied during thermal stimulation of pores of the ampullae of Lorenzini. Heating of the skin near the pore caused a positive potential shift inside the ampullary canal and across the skin (outside with respect to inside) and inhibition of the impulse activity. Cooling of the skin resulted in the opposite effects. Biological significance of the skin mechanism of thermal sensitivity of the ampullae of Lorenzini is discussed.
Doklady Akademii nauk SSSR
Fiziologicheskiĭ zhurnal SSSR imeni I. M. Sechenova
The Journal of General Physiology
Vertebrate rod photoreceptors adjust their sensitivity as they adapt during exposure to steady li... more Vertebrate rod photoreceptors adjust their sensitivity as they adapt during exposure to steady light. Light adaptation prevents the rod from saturating and significantly extends its dynamic range. We examined the time course of the onset of light adaptation in bullfrog rods and compared it with the projected onset of feedback reactions thought to underlie light adaptation on the molecular level. We found that adaptation developed in two distinct temporal phases: (1) a fast phase that operated within seconds after the onset of illumination, which is consistent with most previous reports of a 1-2-s time constant for the onset of adaptation; and (2) a slow phase that engaged over tens of seconds of continuous illumination. The fast phase desensitized the rods as much as 80-fold, and was observed at every light intensity tested. The slow phase was observed only at light intensities that suppressed more than half of the dark current. It provided an additional sensitivity loss of up to 40...
Investigative ophthalmology & visual science
Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology, 2014
Amphibian “green” rods express a blue-sensitive cone visual pigment, and should look yellow. Howe... more Amphibian “green” rods express a blue-sensitive cone visual pigment, and should look yellow. However,when observing them axially under microscope one sees them as green. We used single-cell microspectrophotometry (MSP) to reveal the basis of the perceived color of these photoreceptors. Conventional side-on MSP recording of the proximal cell segments reveals no selective longwave absorbing pigment explaining the green color. End-on MSP recording shows, in addition to the green rod visual pigment, an extra 2- to 4-fold attenuation being almost flat throughout the visible spectrum. This attenuation is absent in red (rhodopsin) rods, and vanishes in green rods when the retina is bathed in high-refractive media, and at wide illumination aperture. The same treatments change the color from green to yellow. It seems that the non-visual pigment attenuation is a result of slender green rod myoids operating as non-selective light guides. We hypothesize that narrow myoids, combined with photome...
Molecular vision, 2009
In a series of works between 1972 and 1984, it was established that rhodopsin undergoes rotationa... more In a series of works between 1972 and 1984, it was established that rhodopsin undergoes rotational and lateral Brownian motion in the plane of photoreceptor membrane. The concept of free movement of proteins of phototransduction cascade is an essential principle of the present scheme of vertebrate phototransduction. This has recently been challenged by findings that show that in certain conditions rhodopsin in the membrane may be dimeric and form extended areas of paracrystalline organization. Such organization seems incompatible with earlier data on free rhodopsin diffusion. Thus we decided to reinvestigate lateral diffusion of rhodopsin and products of its photolysis in photoreceptor membrane specifically looking for indications of possible oligomeric organization. Diffusion exchange by rhodopsin and its photoproducts between bleached and unbleached halves of rod outer segment was traced using high-speed dichroic microspectrophotometer. Measurements were conducted on amphibian (fr...