PubMed Health⌕ Search

Biomedical subjects

G Ramírez

Publications and source records attributed to G Ramírez.

At least 73 records · Page 4Linked to original sources
PubMed1990

Interaction of asymmetric and globular acetylcholinesterase species with glycosaminoglycans.

Chicken muscle and retina, and rat muscle asymmetric acetylcholinesterase (AChE) species were bound to immobilized heparin at 0.4 M NaCl. Binding efficiency was between 50 and 80% for crude fraction I A-forms (AI; muscle), and nearly 100% for fraction II A-forms (AII; muscle and retina). Antibody-affinity-purified AI-forms (chicken) were, however, quantitatively bound to heparin-agarose gels, whereas diisopropylfluorophosphate-inactivated high-salt extracts partially prevented the binding of both AI and AII AChE forms, thus suggesting the presence in crude AI extracts of heparin-like molecules interfering with the tail-heparin interaction. All bound A-forms were progressively displaced from the heparin-agarose columns by increasing salt concentrations, with maximal release at about 0.6 M. They were also efficiently eluted by heparin solutions (1 mg/ml), other glycosaminoglycans being much less effective. Chicken globular AChE forms (G-forms, both low-salt-soluble and detergent-soluble) also bound to immobilized heparin in the absence of salt. Stepwise elution with increasing NaCl concentrations showed maximal release of G-forms at 0.15 M, all globular forms being totally displaced from the column at 0.4 M NaCl. Heparin (1 mg/ml) had the same eluting capacity as 0.4 M NaCl, whereas other glycosaminoglycans were only marginally effective. We conclude that the molecular forms of AChE in these vertebrate species interact with heparin, at salt concentrations that are characteristic for asymmetric and globular forms. Within the A and G molecular form groups, no differences were found in the behavior of the different fractions or subtypes, provided that the enzyme samples were free of interfering molecules.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗
PubMed1989

Compartmentalization of acetylcholinesterase in the chick retina.

Using selective inhibitor treatments, we have studied the distribution of asymmetric (A) and globular (G) forms of acetylcholinesterase (AChE) in the extra- and intracellular compartments of chick retina, a specialized region of chick central nervous system (CNS). Our results show that the chick retinal collagen-tailed AChE (an example of class II asymmetric molecular forms) is essentially an extracellular form of the enzyme; this is the first demonstration of the extracellular localization of asymmetric AChE in the vertebrate CNS. The active site of most of the hydrophobic, membrane-bound G4-form is also exposed to the external environment. In turn, the smaller molecular weight G-forms (G2 and G1) are localized within the cells, where they may represent intermediate components in the assembly or degradation of the more complex enzymatic molecular species. Histoenzymatic ultrastructural techniques show internal AChE in amacrine as well as in ganglion cell bodies, and external enzyme, specifically associated with synapses and axons, in the inner plexiform layer. The probable cooperation of the extracellular A12-forms and the membrane-bound G species (mainly G4) of the enzyme to the hydrolysis of acetylcholine (ACh) released into the external compartment is suggested and discussed.

Acetylcholinesterase↗
PubMed1989

GABAergic modulation of acetylcholine release in cholinergic synaptosomes from Torpedo marmorata electric organ.

GABAA- and GABAB-receptor-specific agonists inhibit the depolarization-evoked release of acetylcholine in cholinergic synaptosomes from Torpedo electric organ. Over 60% of the release is inhibited by a 10(-4) M concentration of GABA itself. IC50s for muscimol and baclofen are 1.3 x 10(-4) and 2.2 x 10(-6) M, respectively. The effect of muscimol is totally blocked by the direct antagonist bicuculline methiodide, and also by the allosteric antagonists methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, picrotoxinin and tert-butylbicyclo-orthobenzoate; the effect of baclofen is blocked by delta-aminovalerate. Furthermore, the inhibitory action of muscimol on acetylcholine release is substantially enhanced by flunitrazepam and pentobarbital. These results suggest the existence of typical GABAA and GABAB receptors in the presynaptic nerve terminals of the Torpedo electric organ regulating the liberation of acetylcholine and therefore the discharge of the electroplaques.

Acetylcholine↗
PubMed1987

Two modes of free migration of amacrine cell neuroblasts in the chick retina.

The migration of amacrine neuroblasts toward the prospective amacrine cell layer in the chick embryo retina has been studied, in Golgi-stained sections, between days 5 and 9 of embryogenesis. Two distinct populations of presumptive amacrine neuroblasts have been identified on the basis of their shape and migratory behavior. One population (smooth amacrine neuroblasts) display smooth, monopolar or bipolar contours, moving freely across the retina without major changes in the original postmitotic shape, and give processes only after reaching the primitive inner plexiform layer. The second population (multipodial amacrine neuroblasts) includes multipolar neuroblasts with abundant filiform and/or lamelliform processes sprouting in various directions; these highly plastic cells begin modifying their shapes at the time of release from the ventricular lining and continue to do so as they move toward their definitive location. Thus, the well-known heterogeneity of adult amacrine cells seems to be preluded by differences in neuroblastic migratory patterns, suggesting the existence of at least two different subsets of amacrine cell precursors.

Animals↗
PubMed1986

Heparin and the solubilization of asymmetric acetylcholinesterase.

Heparin solubilizes asymmetric acetylcholinesterase, from chick skeletal muscle and retina, as a 24 S complex which is quantitatively converted to conventional asymmetric molecular forms of the enzyme (A12 and A8, either class I or class II) upon exposure to high salt. The simultaneous presence of salt and heparin in the homogenization medium selectively prevents, however, the release of class II A-forms in both muscle and retina. Heparin may generally act by displacing native proteoglycans involved in the attachment of the enzyme tail to the extracellular matrix, or its neural equivalent, being in turn removed by salt to yield typical asymmetric enzyme forms. Heparin would also appear to displace some other molecules specifically involved in the EDTA-sensitive attachment of class II tailed forms, this effect being antagonized by salt.

Acetylcholinesterase↗
PubMed1985

Low endemicity and low pathogenicity of rotaviruses among rural children in Costa Rica.

Rotaviruses were prospectively studied in 51 rural Costa Rican children from birth to two years. Samples of feces were collected weekly over a 33-month period. Rotavirus was detected in 45 (1.04%) of 4,317 fecal specimens; 39 infections were documented (an incidence of 0.5 infection per child-year), only five of which were associated with diarrhea (a pathogenicity of 12.8%). Secretory antibody in fecal extracts, detected in six of 39 infections, was short lived and did not protect against reinfection. Serum antibody was present in 69.6% of two-year-old children, but was not detected in 18.8% with documented infections. On the other hand, serum antibody was present in six of 14 children in whom rotavirus was not detected, thus increasing the overall incidence to 0.6 infection per child-year. The combination of prolonged breast-feeding, exposure to a lower infecting dose (compared with urban children), and a higher standard of hygiene than expected may explain the low incidence and low pathogenicity of rotavirus among these rural children.

Age Factors↗
PubMed1983

Fate of collagen-tailed acetylcholinesterase upon extraction of chick retina with salt-detergent solutions in the absence of EDTA.

In chick retina, the tailed 20S molecular form of acetylcholinesterase (A12) is slowly degraded to globular forms after homogenization of the tissue in a buffer-salt-detergent solution, in the absence of EDTA. This process can be stopped by the addition of EDTA to the homogenate, prior to high speed centrifugation; however, longer delays in adding EDTA lead to lower recoveries of tailed enzyme. The rate of degradation of A12 is considerably enhanced by high speed centrifugation of this EDTA-less homogenate prior to addition of EDTA.

Acetylcholinesterase↗
PubMed1983

Enkephalin-like immunoreactivity in Drosophila melanogaster.

Enkephalin-immunoreactive neurons have been identified in the central nervous system of the fruit fly Drosophila melanogaster by immunocytochemical techniques. Analyses of fly extracts by high performance liquid chromatography and radioimmunoassay show a relatively complex pattern of immunoreactive compounds. The most prominent among them has chromatographic properties similar to those of met-enkephalin from which can, however, be distinguished by high-resolution chromatographic techniques.

Animals↗
PubMed1982

Wilms' tumor: histologic grading as a prognostic factor in tumors beyond 10cm in diameter.

The progressive proportion of 25-50 and 75% of undifferentiated cells in the Wilms' tumor mass generate three grading categories: well differentiated (WD); the moderate differentiated (MD) and the poorly differentiated (PD). The Urology Department of the Instituto Nacional de Enfermedades Neoplásicas (Lima, Peru) has studied 60 selected cases registered at its Biostatistics Department. Only 6.9% were well differentiated; 69% were of the poorly differentiated type. In 58 patients our survival rate at two years after diagnosis is higher (39.53%) when the patients are over 2 years of age; while under 2 years of age this survival rate is 26.67%. In a group of 46 patients, the survival rate at two years after initial diagnosis is 44% with a tumor size between 10-14 cm; the survival rate drops to 39.3% when the tumor size is over 15 cm in diameter. There is a linear increasing scale of survival rate for the well differentiated (25%), moderate differentiated (27.3%) and for the patients bearing poorly differentiated types of tumors (48.4%). Further studies are encouraged in order to learn the reasons for this correlation.

Child↗
PubMed1981

Solubilization of collagen-tailed acetylcholinesterase from chick retina: effect of different extraction procedures.

We have extracted acetylcholinesterase from young chick retinas by homogenization in different solutions combining high salt concentration, ionic and nonionic detergents, and EDTA, looking for an optimum procedure for the solubilization of collagen-tailed, asymmetric structural forms of the enzyme. High salt and EDTA seem to be the only necessary requirements for the solubilization of acetylcholinesterase as the A12 form (20S), and the presence of detergent in the homogenization medium does not significantly improve the yield of tailed enzyme. Extraction in the absence of detergent has the potential advantage of a threefold enrichment of tailed enzyme, because only about one-third of the total retinal acetylcholinesterase activity is solubilized. Divalent cations, especially Ca2+, seem to be involved in the attachment of the tailed enzyme to the retinal membranes, at the tail level. High salt-EDTA-extracted 20S acetylcholinesterase (without detergent) aggregates in the presence of exogenous Ca2+ and becomes "insoluble." However, the aggregated 20S acetylcholinesterase can be completely recovered and brought back into solution by further addition of EDTA. Besides, the aggregation can be prevented by the inclusion of Triton X-100 in the homogenization buffer or by adding the detergent concurrently with Ca2+. It is postulated that the acetylcholinesterase collagenous tail is coated by acidic lipid molecules hydrophobically bound to the tail protein so that Ca2+ ionic bridges would actually link these lipid molecules (and consequently the tail) to the membrane matrix. Removal of the lipid coat (e.g., by Triton X-100) produces tailed acetylcholinesterase molecules that no longer aggregate in the presence of Ca2+ and are fully accessible to collagenase digestion.

Acetylcholinesterase↗