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E Popova

Publications and source records attributed to E Popova.

31 records · Page 2Linked to original sources
PubMed1991

The effect of picrotoxin on the absolute and increment retinal sensitivity.

The aim of this study was to investigate the influence of the GABAergic inhibitory neurones on the absolute and increment retinal sensitivity, determined be measuring b-wave threshold of frog electroretinogram (ERG). We found that GABAergic blockade by picrotoxin (PT -noncompetitive GABA antagonist) had no apparent effect on the absolute (dark adapted) b-wave threshold (12 microV criterion amplitude) and slightly, but significantly lowered its increment threshold under both levels of background illumination (0.25 lx and 200 lx), used in this study. A similar effect to that observed in light-adapted eyes was also seen in dark-adapted eyes when suprathreshold stimulus intensities, giving 25 microV b-wave amplitude were presented. Another observation was marked increase of the d-wave amplitude after PT both in dark and light-adapted eyes. We suggest that the different photoreceptor input to the GABAergic interneurones and neurones, responsible for b-wave generation is the cause for the different PT effect on the absolute (rod mediated) and increment (predominantly cone mediated) b-wave threshold of frog ERG. The possible role of the GABAergic inhibitory neurones in the process of light adaptation is discussed.

Animals↗
PubMed1990

Comparative studies on the effects of some enkephalin agonists on the ERG of frog and turtle.

1. Effects of mu-agonist morphine in a concentration of 1.10(-5)-1.10(-6) M and delta-agonist Dalargin in a concentration of 1.10(-5)-1.10(-8) M on electroretinogram (ERG) of frog (mixed type of retina) and turtle (predominantly cone retina) were investigated. 2. The enkephalin agonists studied influenced both types of retina in a different manner, producing mainly inhibitory effects. 3. Variability in mu-receptors sensitivity in the turtle retina, most probably depending on the seasons, was observed. 4. The data obtained show that opiate-sensitive mechanisms control the bioelectric activity of the distal layers of frog and turtle retina. 5. Species specificity and variability in sensitivity of the opiate receptors are discussed.

Animals↗
PubMed1990

GABAergic control on the intensity-response function of ERG waves under different background illumination.

The effect of GABAergic blockade on the intensity-response function of frog ERG waves was investigated under two levels of background illumination in the mesopic and photopic range. GABAergic blockade by picrotoxin shifted the intensity-response curves to the left along the intensity axis and increased their slope under both backgrounds. The maximal gain (dV/dI) and contrast gain (dV/dlog I) of the mechanisms responsible for the ERG wave generation were also increased after GABAergic blockade. The intensity range in which the amplitude of the response was a linear function of the logarithm of the stimulus intensity was very restricted. GABAergic blockade influenced also the rapid transitory processes, which determined the steady-state amplitude of the ERG b-wave after a considerable change of the stimulus contrast. The adaptational effect of the background illumination on the intensity-response function of the ERG waves was not principally changed after GABAergic blockade. The possible neuronal mechanisms of the observed picrotoxin effects are discussed.

Animals↗
PubMed1989

Spectral shifts of cytochrome c oxidase induced by complexons.

Ca2+-chelating agents, such as EDTA and ATP, are shown to bring about a rapid spectral response of the oxidized cytochrome c oxidase due to reversal of the Ca2+-induced red shift of the gamma- and alpha-absorption bands of the ferric enzyme. In addition, complexons are found to bring about Ca2+-independent, slow irreversible spectral changes indicative of a conformational transition of cytochrome oxidase. 1 mol EDTA per mol enzyme is sufficient to produce the maximal effect even in the presence of excess Ca2+, indicating high specificity of interaction. It is suggested that the conformation of cytochrome c oxidase may be regulated by the tightly bound "non-redox' metal ions (Mg, Zn, Cux) known to be present in the enzyme. These ions might be involved in specific binding of physiological effectors with chelating properties, such as ATP.

Adenosine Triphosphate↗
PubMed1989

Picrotoxin effects on frog ERG at different background illumination but same stimulus contrast.

The effect of blockade of GABAergic synapses by picrotoxin on the b- and d-wave of frog ERG was investigated under scotopic (0.002 lx), mesopic (2 lx) and photopic (200 lx) background illumination (Ib). Diffuse white stimuli with two levels of contrast (0.5 and 2.5) were used with each Ib. The aim was to compare the effects of picrotoxin at different background levels, but same stimulus contrast. We found that picrotoxin markedly increased the amplitude and rate of rise of the leading edge of the b- and d-wave with each Ib. This effect was most pronounced at mesopic Ib, smaller at photopic Ib and least pronounced at scotopic Ib. It was relatively stronger on the d-wave than on the b-wave amplitude under scotopic and mesopic conditions. Under photopic conditions, the difference between the picrotoxin effect on the b- and d-wave was much smaller. The possible neuronal mechanisms of the above described picrotoxin effects are discussed.

Animals↗
PubMed1986

A simple assay of the superoxide generation rate with Tiron as an EPR-visible radical scavenger.

Tiron (1,2-dihydroxybenzene-3,5-disulfonate) is oxidized to an EPR-visible semiquinone by superoxide radicals produced by xanthine oxidase. The steady-state level of the Tiron radicals increases with an increased xanthine oxidase concentration. A calibration plot has been obtained relating the steady-state concentration of the Tiron semiquinone determined by EPR-spectroscopy to the rate of 0.2 production as measured by the superoxide dismutase-sensitive cytochrome c reduction. This approach allows for a simple and sensitive assay of 0.2 generation rate in biological systems in the range of ca.0.1-4.0 microM/min using Tiron as a spin trap. The rate of 0.2 generation by antimycin-inhibited ischemic rat heart mitochondria has been measured by this method.

1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium ↗
PubMed1986

Picrotoxin effects on the frog electroretinogram under different background illumination.

The effect of blockade of the GABA-ergic synapses in the frog retina by picrotoxin (PT) on ERG was studied under two conditions of background illumination (Ib): scotopic Ib with illumination level below 0.01 lx and mesopic Ib with illumination level of 2 lx. Under scotopic Ib PT produced a greater relative increase in the d-wave amplitude as compared to the b-wave. The substitution of scotopic Ib by mesopic one in untreated retinas produced a greater decrease in the b-wave amplitude than in the d-wave amplitude. The presentation of the mesopic Ib in PT treated retinas potentiated to nearly the same extent the PT effect on both b- and d-wave. So the initial shift between the amplitudes of the b- and d-wave produced by the mesopic Ib was not significantly altered by PT. The results obtained show that the GABA-ergic neurons in the mixed frog retina participate in the gain control of the ON and OFF channels in a wider range of background illumination. Their relative significance in this control seems to be greater under mesopic Ib than under scotopic Ib. We suggest that the effect of mesopic Ib on the sensitivity of the ERG b- and d-wave is complex and involves some other mechanisms in addition to the GABA-ergic one.

Animals↗
PubMedDate not supplied

[Quantitative determination of immunoglobulins in serum and saliva of patients with denture stomatitis].

A quantitative study on the immunoglobulins G, M, and A in serum and saliva was performed as well as of secretory immunoglobulin A and of the secretory component in the saliva of 35 patients with prosthetic stomatitis and 30 healthy controls without prostheses. The method of radial immune-diffusion in agar according to Mancini, modification of G. Stankova et al. (1983) was used. The study established that there was no statistically significant difference (p greater than 0.05) in the values of immunoglobulins G, M and A in the sera of the subjects from both groups. Statistically significant increase (p less than 0.001) of the values of the immunoglobulin A, secretory immunoglobulin A and secretory component was established in the saliva of the patients with prosthetic stomatitis as compared with the same values in the control group, very likely due to the local reaction of saliva to the present prosthetic constructions.

Adult↗