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Biomedical subjects

V I Govardovskiĭ

Publications and source records attributed to V I Govardovskiĭ.

At least 19 recordsLinked to original sources
PubMed2004

[Visual cycle and dark adaptation: a new approach in research].

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 application of the method for further study of the visual cycle in normal and pathological conditions is discussed.

Amphibians↗
PubMed1988

[A simple highly sensitive recording microspectrophotometer].

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.

Amplifiers, Electronic↗
PubMed1985

[Effect of potassium and calcium channel blockers on changes in the transepithelial potential and spike responses of electroreceptors of the ampullae of Lorenzini in the skate].

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.

4-Aminopyridine↗
PubMed1985

[Effect of liposomes containing antibodies to cyclic nucleotide phosphodiesterase on the receptor potential of rods and cones of the frog retina].

Liposomes loaded with monospecific cGMP-phosphodiesterase (PDE) antibodies act like PDE inhibitors (methylxantins, papaverine) on the aspartate-isolated rod and cone receptor potentials of the isolated perfused rod retina. The response amplitude drastically increases, especially at low stimulus strength, and its time course slows down. Pure lipid liposomes with no antibodies, liposomes loaded with control immunoglobulins, as well as PDE antibodies without liposomes, have no such actions. The effects are readily reversible by wash-out, which implies the liposome + antibodies action without penetrating the cells. The increase in the response amplitude can be only partly explained by the measured increase in the extracellular resistance of the photoreceptor layer under liposome action. It is supposed that the specific adsorption of liposomes on the photoreceptor cell surface changes the function of the intracellular transmission mechanism or (and) the properties of ionic channels of the plasma membrane in yet unknown way.

1-Methyl-3-isobutylxanthine↗
PubMed1984

[Reactions of the ampullae of Lorenzini of the skate to electric stimulation after polarization of the receptor epithelium].

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.

Animals↗
PubMed1983

[Study of the receptor mechanisms of the electroreceptors of ampullae of Lorenzini in the skate].

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.

Animals↗
PubMed1983

[Electrical model of the electroreceptor of the ampulla of Lorenzini].

An electrical model is proposed for the Lorenzinian ampulla receptor epithelium. The model is based on the authors' experimental results and explains most of the experimental data available in literature, including an unusual sign of spike response in afferent fibres and complex patterns of electroreceptor responses to the applied stimuli. Its main assumption is an N-shaped voltage-current relation of the receptor cell apical membrane possessing, within the range of operation, a stationary negative-slope resistance.

Animals↗
PubMed1982

[Changes in the transepithelial potential and spike responses of the ampullae of Lorenzini to temperature stimulation in the skate].

Electrical responses of the sensory epithelium of Lorenzinian ampullae as well as their nerve fibres frequency reactions to thermal stimulation were studied in Black Sea skates, Raja clavata. Electrically isolated ampullae with input resistance 500-800 K omega were used. They were loaded through a feedback circuit to a controllable resistance. Heating of the ampulla caused a lumen-negative shift of the transepithelial potential, its amplitude being approximately linearly dependent on the input resistance of the preparation (R1). Frequency responses of the nerve fibres were also dependent on R1. With R1 more (less) than 400-500 K omega there was an increase (decrease) in spike frequency during heating of the ampulla. Two temperature-dependent potential sources in sensory epithelium affecting spike frequency in the opposite ways are suggested.

Animals↗
PubMed1981

Light-induced changes of cyclic GMP content in frog retinal rod outer segments measured with rapid freezing and microdissection.

Cyclic GMP concentration was measured in the rod outer segments (ROS) of the isolated frog retinas. Retinas were quickly frozen in 0.5 s after the short light flash producing 90%-saturated late receptor potential (2,000 rhodopsins bleached per rod). ROS were obtained by microdissection, the cGMP levels were determined by radioimmunoassay method. No detectable changes in cGMP concentration was found in this stimulus condition. Dark-adapted ROS contained 46.3 +/- 2 pmol/mg. 3-s bright illumination (ca. 10(7) rhodopsins bleached per rod per second) led to approximately 30% drop in cGMP content. It is supposed that the main part of cGMP with the ROS is in the bound state and therefore fast light-induced changes in its minor free fraction may escape the detection.

Animals↗
PubMed1981

[Cutaneous mechanism of the temperature sensitivity of ampulla of Lorenzini electroreceptors].

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.

Animals↗
PubMed1980

[Mechanism of temperature sensitivity of ampulla of Lorenzini electroreceptors].

In acute experiments on the Black sea skates (Raja clavata) the transepithelial potential of Lorenzinian ampullae and impulse activity of their single nerve fibres were studied during electrical and thermal stimulation. The potential inside the canal and input resistance of the ampulla were 0 divided by -2 mV and 250-400 k omega respectively. Heating of the capsule was accompanied by a negative wave of the potential, an increase in the ampulla resistance and a decrease in spike frequency. Cooling of the preparation caused the opposite changes in the parameters. Waves of the transepithelial potential are supposed to reflect changes in the potential difference across the basal membrane of a receptor cell, which is hyperpolarized by heating.

Animals↗
PubMed1978

[Structural and functional organization of the vestibular apparatus in rats maintained under weightless conditions for 19.5 days aboard the satellite "Cosmos-782"].

Vestibular apparatus was investigated in rats subjected to weightlessness for 19.5 days in the satelite "Cosmos-782" and experienced acceleration on launching and landing. Some structural and functional changes were noted. They were seen in otolith clinging to the utricular receptor surface and in the peripheral arrangement of the nucleolus in the nuclei of the receptor cells. It is also possible that increased edema of the vestibular tissue resulted in destruction of some receptor cells, and within the otolith--changes in the form and structure of otoconia. In the horizontal crista the cupula was separated.

Acceleration↗