Study of taurine and tauret content in the compound eye of locust with light and dark adaptation.

Taurine as well as tauret (retinyliden taurine) levels were measured in locust Locusta migratoria compound eyes. HPLC measurements revealed relatively low taurine levels (1.9 +/- 0.16 mM) in dark-adapted eyes. Glutamate, aspartate and glycine levels were 2.0 +/- 0.2, 2.7 +/- 0.4 and 3.0 +/- 0.37 mM, respectively, while GABA was present only in trace amounts. After about 4 h of light adaptation at 1500-2000 lx, amino acid levels in the compound eye were as follows: taurine, 1.8 +/- 0.17 mM; glutamate, no change at 2.1 +/- 0.2 mM; aspartate sharply increased to 4.7 +/- 0.7 mM; glycine slightly decreased to 2.8 +/- 0.3 mM; and GABA trace levels. In the compound eye of locust Locusta migratoria, the existence of endogenous tauret in micro-molar range was established. In the dark, levels were several times higher compared with compound eye after light adaptation 1500 lx for 3 h, as estimated by TLC in combination with spectral measurements. Existence of tauret in compound eye is of special interest because in the compound eye, rhodopsin regeneration is based on photoregeneration.

[Lectin-enzyme assay as a method of estimation of immunoglobulins' glycosylation].

The mechanism of interaction of lectins with IgG molecules by the method of the lectin-enzyme assay has been described that allows to register a degree of human serum IgG molecules' glycosylation (mannosylation in case of lectin of Pisum sativum) in norm and at pathology. To detect an authentic difference in a glycosylation degree between control and pathological IgG, the wells of an ELISA plate were coated with an antibody in concentration of 1 microg/ml. Introducing alpha-D-mannose between the stages of incubation of immunoglobulin and lectin showed, that alpha-D-mannose inhibits the affinity of lectins for IgG. The preliminary incubation of lectin with IgG molecules stabilizes the activity of horseradish peroxidase, which labeled the lectins. Lectin-enzyme assay, in which Fab and Fc fragments of IgG were used, showed that lectin of Pisum sativum possesses a higher affinity for Fab regions. These findings and the glycosylation analysis of paraproteins and Bence-Jones proteins of multiple myeloma patients help to understand the details of interaction of immunoglobulins and lectins.

Taurine as a universal carrier of lipid soluble vitamins: a hypothesis.

In the literature taurine is characterized as a non-specific growth or blood clotting factor, an antioxidant, a membrane protector, or a regulator of calcium ion homeostasis, just as vitamins A, D, E, F, and K are similarly characterized. On the basis of recent finding concerning the relationship between taurine and the aldehyde of vitamin A-retinal (Petrosian and Haroutounian, 1988, 1998; Petrosian et al., 1996), as well as on the basis of data from the literature, we now suggest a hypothesis that taurine promotes the bioavailability of the lipid soluble vitamins A, D, E, K, and F, probably by forming different types of water soluble, easily hydrolyzable complexes. It is quite possible that the ability of taurine to convert lipids and lipid soluble substances into a water soluble state is the key to understanding the unusually wide diversity of biological phenomena associated with taurine. This form of delivery may be an additional, secondary mechanism for the transport of lipid soluble vitamins, which was probably acquired early in evolution, and remains extremely important for mammals and humans directly after birth for a variety of physiological functions such as: vision in normal and in emergency situations, rapid blood clotting, sperm eruption, and situations requiring a prompt consumption of lipid soluble vitamins characteristic of excitable systems. Clearly, the role of taurine in the physiology of the water insoluble vitamins remains an enigma and is worthy of further investigations.

Effects of osmotic and light stimulation on 3H-taurine efflux from isolated rod outer segments and synthesis of tauret in the frog retina.

After injection of 3H-taurine into eyeballs of frogs and maintenance for 3 h in darkness by a gentle shaking, an almost homogenous fraction of rod outer segments (ROS) was prepared. About a 22% decrease in tonicity caused by reducing NaCl in isotonic 225 mOsm normal solution caused a rapid increase in the rate coefficient of efflux of 3H-taurine from the ROS fraction. The peak level of increased efflux rate coefficient was 7-times higher than the basal isotonic level. This indicates that taurine could contribute essentially to the volume regulation, either via selective channels or a carrier transporter-mediated pathways. For further clarifying if taurine fluxes in the ROS are sensitive to the light, other experiments were performed. Neither light stimulation of dark-adapted ROSs fractions or dark stimulation of weakly illuminated ROSs revealed any detectable changes in the efflux rate coefficient of 3H-taurine. These results indicate that light-induced taurine efflux, if present in the ROS, must be small, compared with hypoosmotic induced efflux. Thus the question of light-induced release of taurine from ROS still remains to be clarified. In the second part of this study, using TLC (thin layer chromatography) in combination with 3H-taurine measurements we have tried to clarify whether frogs (Rana ridibunda) eye structures can synthesize tauret (retinylidenetaurine). In isolated retinal preparations almost no any noticeable radioactivity was detected compared with background level. The capability of the eye structures to synthesize tauret from 3H-taurine was revealed in the second whole eye injection experiment. About 0.3% of the total 3H-taurine pool taken up was converted into 3H-tauret in the dark-adapted frog retina. In the retina of frogs adapted to light compared with those which were dark adapted tauret quantities were remarkable lower--on average about half. These results are in agreement with our recent data obtained by HPLC, which indicate tauret levels several times higher in the dark-adapted frog retinae compared with those after long lasting light adaption. Taking into account these results one can conclude that the main structure able to synthesize 3H-tauret is probably pigment epithelium rather than retina.

New HPLC evidence on endogenous tauret in retina and pigment epithelium.

This investigation was improve the separation for tauret (retinylidene taurine) and to compare its content in the retina under dark and light adaptation. To prevent tauret hydrolysis, retinal samples were quickly frozen and lyophilized. Methanol extracts of dried retina and pigment epithelium from both dark- or light-adapted frogs, Rana ridibunda, were injected onto HPLC. Synthetic standard tauret appeared at 4.7 min after the solvent front. At the same time, an endogenous substance was eluted from the mixed retinal and pigment epithelial samples. The UV spectra of this endogenous compound matched with the spectra of synthetic tauret obtained under identical conditions, with lambda(max) = 446 nm at peak. We conclude that the HPLC system used permitted full separation of tauret from the methanol extracts of the retina and pigment epithelium. TLC and further HPLC analysis have shown that tauret quantities were several times higher in the retina and pigment epithelium of the frogs adapted to dark compared with those light-adapted (about 4 h under 1000 1x illumination). Tauret based vitamin A transport is probably involved in other systems as well, where along with its other known beneficial effects taurine probably is necessary to facilitate vitamin A transport.

The role of taurine in osmotic, mechanical, and chemical protection of the retinal rod outer segments.

The ability of the photoreceptor cell to resist osmotic stress was examined by incubating isolated frog retina in medium of varying osmolality. An electron microscopic analysis of the rod outer segment following a severe hypoosmotic insult revealed connections between adjacent disks and between disk rims and the plasma membrane, which presumably provide mechanical stability to the rod outer segment. One surprising result was the extent of the damage incurred by the electrical signaling pathway of the photoreceptor cells subjected to a 50 mOsm insult; only the distal P111 component of the ERG remained unaffected. Thus, the rod outer segment is particularly resistant to osmotic-induced injury, presumably because of the effective osmoregulatory actions of taurine. Incubation of retina with tauret, retinylidentaurine, uncovered rose-like hexagonal structures on the surface of the rod outer segment. These structures purportedly consist of connections between disk rims and the plasma membrane of the rod outer segments. Based on the influence of tauret, it is likely that the calcium dependence of these channels is selective for retinoids. These data are discussed relative to taurine's role in the process of rhodopsin regeneration and in the protection of the rod outer segments against osmotic, mechanical and light induced damage.

Effects of taurine and light on retinal GABA content and the efflux of 14C-GABA and 14C-aspartate from frog retina.

GABA content of isolated, dark adapted frog retina was found to be 3.15 +/- 0.28 mM. After 30 minutes of exposure to intense light (200 lx), retinal GABA levels increased about 70%. Interestingly, incubation of dark adapted retina for 30 minutes with medium containing 0.4 mM taurine also led to a 70% increase in GABA levels. Since the light-induced elevation in GABA content was reduced over 50% by a simultaneous injection of 0.02 mM strychinine, it is likely that the light-induced GABA change is partly mediated by the release of taurine from the retina seen after light exposure. However, incubation of isolated retina with medium containing increasing concentrations of taurine (1, 2 and 20 mM), caused a progressive rise in 14C-GABA efflux from retina that was preloaded with 2.2 microM GABA and exposed to dim light (0.05 lx). It was also shown that taurine (1 and 5 mM) dramatically reduced 14C-aspartate efflux from retina preloaded with radioactive aspartate and exposed to dim light conditions. By comparison, intense light stimulation (40 lx) reduced basal 14C-aspartate efflux while dark exposure increased 14C-aspartate loss from the isolated retina. We found that taurine depressed the b-wave signal of frog retina, with the maximum effect occurring at a concentration of 1 mM. Addition of strychnine (0.4 mM) reversed the taurine effect on the b-wave, indicating that taurine receptors must be present in the inner retina. By contrast, taurine (0.1-20 mM) had no effect on the P111 component of the ERG initiated by either aspartate or cobalt. However, taurine exerted a modest depressant activity on P111 initiated by glutamate. The significance of these data relative to the putative neurotransmitter function of taurine in the inner retina is discussed.

[Phospholipid-phospholipid relations and changes of free radical lipid oxidation in biological membranes during alloxan diabetes]. / Izuchenie fosfolipid-fosfolipidnykh sootnoshenii i dinamiki svobodnoradikal'nogo okisleniia lipidov v biologicheskikh membranakh pri alloksanovom diabete.

Quantitative and qualitative composition of phospholipids as well as lipid peroxidation were studied in outer and inner mitochondrial membranes and microsomal fraction from rat liver tissue under conditions of alloxane diabetes. In the diabetes amount of phospholipids, mainly cardiolipins and phosphatidylethanolamines, was increased in the inner and decreased in the outer mitochondrial membranes. Phosphatidylcholines and phosphatidylserines were increased in microsomal fraction. At the same time, lipid peroxidation was activated both in ascorbate- and NADPH-dependent systems of oxidation. These data suggest that lipid peroxidation affects the composition of mitochondrial membranes either by means of removing of the substances from membranes or via their redistribution between the subcellular fractions.

[Effect of the level of lighting on 14C-GABA efflux from the isolated retina of the frog Rana ridibunda]. / O vliianii urovnia osveshchennosti na potok 14C-GAMK iz izolirovannoi setchatki liagushki Rana ridibunda.

Studies have been made of the effect of changes in illumination levels on 14C + GABA efflux in the isolated retina of the frog R. ridibunda. When the retina loaded with 14C-GABA is stimulated by darkness, the efflux of radioactivity immediately increases. After reaching a peak, the efflux of 14C-GABA slightly decreases attaining steady level which is higher than the level of spontaneous efflux observed during weak (approximately 0.05 lux) illumination. This high level is preserved as long as the retina remains in darkness. During illumination of the retina (transition from darkness to 60 lux), two types of response are observed. In some cases, insignificant increase of GABA efflux from the retina is followed by its rapid decrease up to the level which is observed during weak illumination. In other cases, immediately after illumination the decrease in GABA efflux takes place (in 6 experiments out of 10). In accordance with the data of Voaden [6], it is suggested that 14C + GABA is liberated from horizontal and amacrine cells. The data obtained in the present investigation are discussed in terms of Trifonov [14] and Byzov [15] hypothesis. These data confirm the idea that GABA acts as a retinal neurotransmitter in the frog.

[Effect of gamma-aminobutyric acid on the concentration of noradrenaline in the synaptosoma fraction of the meso-diencephalic region of rat brain]. / Deistvie gamma-aminomaslianoi kisloty na soderzhanie noradrenolina v sinaptosomal'noi fraktsii mezo-diéntsefalicheskoi oblasti mozga krys.

We had previously shown [1, 2, 3, 4] that intraperitoneal administrations of 5 mg/kg amounts of gamma-aminobutyric acid (GABA) lower norepinephrine (NE) level of rat brain, this effect being most pronounced in the hypothalamic region. Subsequent studies showed that GABA increased normetanephrine level in iproniazid pretreated rats (II) and decreased NE content of crude mitochondrial fractions (12). These data implied changes in NE content of nerve endings. The results of the present study indicate that the NE content of the synaptosomal fraction of the mesodiencephalic region of GABA treated rats is significantly lower than that of untreated animals. This is a further confirmation of our previous results favouring a release of NE from nerve endings following the administration of GABA.