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Biomedical subjects

R Salceda

Publications and source records attributed to R Salceda.

At least 37 records · Page 2Linked to original sources
PubMed1991

Neurochemical effects of nicotine on glutamate and GABA mechanisms in the rat brain.

The effects of nicotine on gamma-aminobutyric acid (GABA) and glutamate mechanisms were studied in several rat brain regions both in vivo and in vitro. In vivo acute intermittent injections of nicotine decrease GABA utilization in the hypothalamus and glutamate levels within the nucleus caudatus and the subcortical limbic forebrain (mainly tuberculum olfactorium and nucleus accumbens). Glutamic acid decarboxylase activity was slightly increased in several regions, when the rats were treated with a single convulsant dose of nicotine and killed at the moment of the convulsions but it was not affected by a single injection nor by intermittent acute administration of non-convulsant doses of nicotine. In vitro nicotine elicited release of L-[3H]glutamate from synaptosomal preparations obtained from the frontoparietal cortex, nucleus caudatus and hypothalamus. The effect was dose-dependent and it was not blocked by mecamylamine. It was also Ca2+ independent. The possibilities are discussed that the decreased GABA utilization in the hypothalamus may be related to certain neuroendocrine actions of nicotine and that the nicotine-induced glutamate release might be involved in some of the physiological and toxicological effects of nicotine.

Animals↗
PubMed1990

Characterization of calcium uptake in chick retinal pigment epithelium.

45Ca uptake was studied in isolated chick retinal pigment epithelial cells. 45Ca was accumulated by a saturable, temperature-dependent system with a KM of 400 microM and a Vmax of 0.13 mumoles2mg protein/min, which depends on the external sodium concentrations. The transport system was present early during embryonic development. RPE cells of three breeds of chicks with different degrees of pigmentation accumulated calcium proportionally to the melanin content of the cells, suggesting that pigment granules participate in the storage and regulation of intracellular calcium.

Animals↗
PubMed1989

A glutamate dehydrogenase-based method for the assay of L-glutamic acid: formation of pyridine nucleotide fluorescent derivatives.

A method for the quantitation of L-glutamic acid in the picomole range was developed by finding conditions which allowed the production of NADH by the action of the L-glutamate dehydrogenase (EC 1.4.1.3) and its subsequent transformation to a highly fluorescent derivative. The method measures linearly glutamate from 250 pmol to 5 nmol. For its simplicity and low cost it is ideally suited to the assay of a large number of samples within a single working day. Its application to the determination of regional glutamate levels in the rat brain, as well as to the measurement of ornithine aminotransferase (EC 2.6.1.13) activity from several tissues is described. The results are similar to those obtained by different methodologies in several laboratories, but the present method offers additional advantages.

Animals↗
PubMed1989

Uptake and K+-stimulated release of [14C]glycine from frog retinal synaptosomal fractions.

The uptake of [14C]glycine and the effect of depolarizing potassium concentrations on its release was investigated in the whole frog retina and its synaptosomal fractions. The uptake of [14C]glycine in retina and synaptosomal fractions was found to be saturable as well as energy and Na+-dependent. The Km value for glycine uptake was found to be 46 microM for P2 fraction and 100 microM for P1 fraction, with a Vmax of 3.5 and 3.8 nmol/mg protein/min respectively. The release of [14C]glycine from P1 and P2 synaptosomal fractions was markedly increased by raising potassium concentration in the medium, in a partially Ca2+-dependent manner. Evoked glycine release was 50% reduced when calcium was omitted from the medium. The K+-stimulated release of glycine from P2 fraction was significantly reduced in the presence of TTX. The cellular origin of the P1 and P2 synaptosomal fractions releasing glycine is discussed.

Animals↗
PubMed1989

45Ca uptake by retinal pigment epithelial cells.

Uptake of 45Ca was studied in isolated frog retinal pigment epithelial cells. 45Ca accumulation was found to be a saturable, temperature-dependent event. Kinetic analysis of this accumulation revealed two transport systems with apparent km of 2.0 and 0.3 mM. We found the presence of a Na-Ca exchanger mechanism that releases Ca2 under depolarized conditions. Light induced an increase of 45Ca uptake due to activation of the Na-K-ATPase and consequent decrease of extracellular potassium concentration.

Animals↗
PubMed1986

Isolation and biochemical characterization of frog retinal pigment epithelium cells.

The structure and function of the photoreceptor cell depends on the renewal of its outer segment. Phagocytosis of the rod outer segments by RPE is an essential part of the renewal process. Several methods have been reported in order to isolate RPE cells; however, the isolated cells are heavily contaminated by other cell types, mainly erythrocytes and rod outer segments. The primary aim of this study was the isolation of pure and viable frog RPE cells. Cells were dissociated in a calcium-free Krebs bicarbonate medium and purified by centrifugation in a ficoll density gradient. Viability of the purified cells assessed by trypan blue dye exclusion was 95%. The metabolic activity of the cells was tested by several parameters: RPE cells consume oxygen at a rate of 11.5 ngatoms/min/mg protein, transport and metabolize 14C-glucose by a sodium dependent mechanism, and are able as well to accumulate 14C-leucine and incorporate it into proteins. Results obtained in this study indicate that our isolation procedure yields a more intact preparation of RPE than those described previously; hence, it may be helpful in elucidating the biochemical and metabolic parameters involved in pigment epithelium physiology.

Animals↗
PubMed1985

Effect of light on Na-Ca exchange in rod outer segments in frog.

The effect of illumination on the calcium (Ca) translocation mechanisms in isolated frog rod outer segments (ROS) was studied. The ATP-dependent Ca uptake and the Ca-Ca exchange mechanisms were unaffected by light. In contrast, we report a light-evoked Ca efflux which is mediated by the Na-Ca exchange system. The ratio of released Ca to rhodopsin bleaching was measured and the stoichiometry obtained was 5 Ca molecules released per mole of rhodopsin bleached. Concomitant to the Ca release, light induced Ca uptake, which increase the total Ca content of ROS. Physiological relevance of results to the phototransduction process is discussed.

Adenosine Triphosphate↗
PubMed1982

Uptake, release, and binding of taurine in degenerated rat retinas.

High-affinity uptake, potassium-stimulated release and receptor binding of gamma-aminobutyric acid (GABA) and taurine were studied in retinas of rats treated with monosodium glutamate (MSG) or iodoacetate-malate (IAM). Such treatments produce a selective damage of the inner retinal layers (MSG) or of the photoreceptor layer (IAM). MSG treatment decreased GABA uptake by more than 60%. Also, the potassium-stimulated release of this amino acid was markedly diminished (90%) in retinas lesioned by MSG. MSG treatment decreased 3H-GABA binding by 45%. Uptake, release or binding of GABA were unaffected by IAM-treatment. Taurine uptake was reduced by a similar degree by both MSG and IAM treatment, 57% and 38% respectively. Potassium-stimulated release of taurine was unchanged by MSG and 50% reduced by IAM. Both treatments reduced the spontaneous release of endogenous taurine. Binding of taurine to receptors in retinal membranes was practically unaffected by any of the treatments utilized. These results are consistent with a neurotransmitter action of GABA at the inner retinal layers, while they do not support a major role for taurine as a synaptic transmitter in retina.

Animals↗
PubMed1982

Nucleotide content of isolated bovine rod outer segments.

Endogenous nucleotide levels of isolated intact ROS were analyzed by high pressure liquid chromatography. Intact bovine ROS showed a total nucleotide concentration of 1.0 mM, ATP and GTP being the major components (0.1-0.2 mol per mol of rhodopsin). When intact ROS resuspended in sucrose-ficoll medium were diluted in a Ringer-Krebs bicarbonate, the nucleotide ratios were markedly changed, but the total concentration remained unchanged. The concentration of cyclic nucleotides (cAMP and cGMP) was markedly enhanced when ROS were placed in Ringer buffer, whereas ATP and GTP concentration was reduced. Total nucleotide concentration is 100% higher in intact than in leaky plasma membrane ROS. Upon illumination, no change was observed in the nucleotide levels of ROS in sucrose-ficoll medium. However ATP, GTP and cAMP levels were reduced when ROS in Ringer medium were exposed to light while cGMP concentration showed no change. Relevance of relative nucleotide content and ionic concentration to the transduction phenomenon in photoreceptor is discussed.

Adenosine Triphosphate↗
PubMed1980

High-affinity taurine uptake in developing retina.

A specific system for taurine transport is present at the early stages of development in both chick and rat retinas. The results obtained with taurine analogs indicate a high degree of specificity of taurine uptake. Two transport systems were detected for the adult rat retina: a high-affinity (Km 21 microM) and a low-affinity transport system (Km 312 microM). On the other hand, in the adult chick retina, only a low-affinity transport system (Km 580 microM) could be detected. Nevertheless, embryo chick retina accumulated [3H]taurine by two different kinetic mechanisms with Kms of 242 microM and 21 microM for the low- and high-affinity processes, respectively. Taurine uptake systems were absolutely Na+ dependent. The sodium-dependence curve for taurine uptake was sigmoid. These mechanisms appear not to be mediated by a Na+ cotransport system. In spite of the differences observed in taurine uptake in both species, in each of them it closely parallels the changes brought about by the morphological and functional maturation of the retina.

Aging↗
PubMed1980

The effect of colchicine and cytochalasin B on the release of taurine from the chick retina.

The effect of colchicine (0.5 mM) and of cytochalasin B (10(-4) M) on the release of [35S]taurine from the isolated chick retina, upon stimulation by 68.5 mM-KCl, 10(-5) M-veratridine, and 10 mM-glutamate, was studied. Cytochalasin and colchicine effects on taurine release were compared with those on K+-stimulated release of [3H]dopamine and [3H]GABA. Colchicine caused a marked decrease of the [35S]taurine release evoked by the three stimulatory agents; it also decreased [3H]dopamine release without affecting that of [3H]GABA. Cytochalasin B significantly decreased the efflux of [35S]taurine stimulated by glutamate or veratridine without altering that evoked by 68.5 mM-KCl. Cytochalasin practically suppressed the [3H]dopamine-stimulated release and slightly decreased that of [3H]GABA. This drug produced a high increase in the spontaneous release of labeled GABA and taurine. These results suggest that the release of taurine and GABA from the chick retina probably occurs though different mechanisms. It is suggested that taurine release may be related to a process involving contractile proteins.

Animals↗
PubMed1979

Glutamate decarboxylase activity in chick brain and retina. Inhibition of the immature enzyme by Triton-X-100.

We have studied the effect of Triton-X-100 on glutamate decarboxylase (GAD) activity in brain and retina from chick embryos of 12 and 16 days' incubation and from chicks 4--6 weeks old. GAD activity was measured in five different homogenization media. Triton-X-100 inhibited the enzyme by about 60% in both brain and retina of 12-day embryos and by about 50% in 16-day embryos, independently of the homogenization medium. In chicks only about 20% inhibition by the detergent was observed in brain whereas no effect was found in retina. These results indicate that the evaluation of the experimental conditions of enzyme assays at different ages is essential for developmental studies of GAD activity in nervous tissue.

Aging↗
PubMed1978

Potassium-stimulated release of GABA, glycine, and taurine from the chick retina.

The effect of depolarizing potassium concentration on the release of [14C]glycine, [3H]GABA, and [3S]taurine was investigated in the whole chick retina and in a synaptosomal fraction prepared from the chick retina. In the whole retina, increasing potassium concentration above 40 mM resulted in an increased release of the three amino acids. The release of glycine was the most stimulated and that of taurine, the least. The potassium-evoked release of glycine and GABA was calcium dependent. In the synaptosomal fraction, 68.5 mM potassium significantly stimulated the efflux of GABA and glycine by a calcium-dependent mechanism. The release of taurine from this fraction was unaffected by high potassium.

Animals↗
PubMed1976

Cysteine sulphinate decarboxylase in chick and rat retina during development.

The activity, properties and developmental pattern of cysteine sulphinate decarboxylase (CSD) were studied in chick and rat retina. Retinal CSD shows properties similar to those of the enzyme in brain with respect to optimum pH, saturating substrate concentrations and stimulation by pyridoxal phosphate, CSD activity increased 3-fold from the 10th day of embryogenesis to hatching in chicks and in postnatal development in rats. The developmental pattern of CSD activity in both species is coincident with the functional maturation of visual function.

Aging↗