Efecto del plomo y del arsénico en condiciones de laboratorio sobre la rana africana de uñas (Xenopus laevis) y la rana leopardo (Lithobates berlandieri) / Effect of lead and arsenic under laboratory conditions on African clawed frog (Xenopus laevis) and leopard frog (Lithobates berlandieri)

Actualmente, existe una creciente preocupación ya que algunas especies de anfibios han mostrado un declive en sus poblaciones por causa de diversos factores, entre ellos los metales pesados; por esta razón, es importante realizar estudios sobre esta problemática ambiental. El objetivo de este estudio fue determinar la cantidad del plomo y arsénico que se concentra en los tejidos de la rana Africana de uñas (Xenopus laevis) en etapa juvenil y de la rana Leopardo (Lithobates berlandieri) en etapa larvaria y en el agua después de 16 semanas expuestas a placas de plomo y arseniato de sodio, con la finalidad de determinar si esta acumulación de metales provoca eventualmente anomalías morfológicas en su desarrollo. Los individuos fueron puestos en contacto con placas de plomo, arseniato de sodio, agua de la red de abastecimiento de agua de consumo público (grupos experimentales) y con agua potable (grupo control). Los organismos fueron inspeccionados de manera externa para identificar anomalías macroscópicas, además de realizarles análisis morfométricos. Los análisis espectroquímicos (espectrofotometría de absorción atómica, con la técnica de horno de grafito) mostraron que hay un proceso de bioconcentración y bioacumulación de metales cuando los organismos están en contacto con estos metales y con agua de la red de abastecimiento público, la cual está contaminada también, pues se detectaron cantidades altas de metales en los tejidos de las larvas. Respecto a la morfometría hubo diferencias significativas en algunas estructuras entre el grupo control y los grupos experimentales en X. laevis. En L. berlandieri fueron detectadas anomalías macroscópicas como curvatura de la cola, problemas de pigmentación, protuberancias en el abdomen e inadecuada posición de los intestinos en aquellos individuos que estuvieron en contacto con estos metales pesados. (AU)

Currently, there is growing concern as some amphibian species have shown a decline in their populations due to various factors, including heavy metals; for this reason, it is important to carry out studies on this environmental problem. The objective of this study was to determine the amount of lead and arsenic concentrated in the tissues of the African clawed frog (Xenopus laevis) in the juvenile stage and the Leopard frog (Lithobates berlandieri) in the larval stage and in the water after 16 weeks exposed to lead plates and sodium arsenate, in order to determine if this accumulation of metals eventually causes morphological abnormalities in their development. The individuals were placed in contact with lead plates, sodium arsenate, water from the public water supply network (experimental groups) and with drinking water (control group). The organisms were externally inspected to identify macroscopic anomalies, in addition to performing morphometric analysis. The spectrochemical analyzes (atomic absorption spectrophotometry, with the graphite furnace technique) showed that there is a process of bioconcentration and bioaccumulation of metals when the organisms are in contact with these metals and with water from the public supply network, which is also contaminated, since high amounts of metals were detected in the tissues of the larvae. Regarding morphometry, there were significant differences in some structures between the control group and the experimental groups in X. laevis. In L. berlandieri, macroscopic abnormalities such as curvature of the tail, pigmentation problems, protuberances in the abdomen and inappropriate position of the intestines were detected in those individuals that were in contact with these heavy metals. (AU)

Rapid stimulation of human renal ENaC by cAMP in Xenopus laevis oocytes

Among the compensatory mechanisms restoring circulating blood volume after severe haemorrhage, increased vasopressin secretion enhances water permeability of distal nephron segments and stimulates Na+ reabsorption in cortical collecting tubules via epithelial sodium channels (ENaC). The ability of vasopressin to upregulate ENaC via a cAMP-dependent mechanism in the medium to long term is well established. This study addressed the acute regulatory effect of cAMP on human ENaC (hENaC) and thus the potential role of vasopressin in the initial compensatory responses to haemorrhagic shock. The effects of raising intracellular cAMP (using 5 mmol/L isobutylmethylxanthine (IBMX) and 50 ìmol/L forskolin) on wild-type and Liddle-mutated hENaC activity expressed in Xenopus oocytes and hENaC localisation in oocyte membranes were evaluated by dual-electrode voltage clamping and immunohistochemistry, respectively. After 30 min, IBMX + forskolin had stimulated amiloride-sensitive Na+ current by 52 % and increased the membrane density of Na+ channels in oocytes expressing wild-type hENaC. These responses were prevented by 5 ìmol/L brefeldin A, which blocks antegrade vesicular transport. By contrast, IBMX + forskolin had no effects in oocytes expressing Liddle-mutated hENaC. cAMP stimulated rapid, exocytotic recruitment of wild-type hENaC into Xenopus oocyte membranes, but had no effect on constitutively over-expressed Liddle-mutated hENaC. Extrapolating these findings to the early cAMP-mediated effect of vasopressin on cortical collecting tubule cells, they suggest that vasopressin rapidly mobilises ENaC to the apical membrane of cortical collecting tubule cells, but does not enhance ENaC activity once inserted into the membrane. We speculate that this stimulatory effect on Na+ reabsorption (and hence water absorption) may contribute to the early restoration of extracellular fluid volume following severe haemorrhage (AU)

Cholinergic currents in Xenopus oocytes transplanted with human brain membranes

Corrientes colinérgicas de cerebro humano fueron registradas en oocitos de Xenopus laevis trasplantados con membranas de cerebro humano procedentes de dos zonas diferentes, la corteza frontal y el hipocampo. Las corrientes registradas fueron activadas por el receptor nicotínico o por el receptor nicotínico o muscarínico de la acetilcolina. Se probaron los efectos de diferentes agonistas nicotínicos como acetilcolina, nicotina y yoduro de 1,1-dimetil-4-fenil-piperazinio (DMPP), y antagonistas del receptor nicotínico como a-bungarotoxina y d-tubocurarina en los oocitos transplantados. Detectamos cuatro clases de cinéticas de corrientes nicotínicas. Las diferencias en la amplitud y en la carga eléctrica total de las corrientes provocadas por varios agonistas en el rango de potencial mantenido no fueron significativas, excepto en el caso del DMPP a un potencial mantenido de -90 mV. Nuestros resultados indican que las formas alfa4beta2, alfa3beta4 y alfa7 son los principales receptores nicotínicos en el cerebro humano

Cholinergic human brain currents were recorded in Xenopus laevis oocytes transplanted with human cerebral membranes from two different zones, the frontal cortex and the hippocampus. The recorded currents were supported by the nicotinic or the muscarinic acetylcholine receptor. We tested the effects of a number of several nicotinic agonists acetylcholine, nicotine and 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), and the nicotinic receptor antagonists a-bungarotoxin and d-tubocurarine on the transplanted oocytes. We detected four kinds of nicotinic current kinetics. The differences in the amplitude and in the total electric charge of the currents elicited by various agonists at a range of holding potentials were not significant, except in the case of DMPP at a holding potential of -90 mV. Our results indicate that alpha4beta2, alpha3beta4 and alpha7 are the main nicotinic receptors in human brain

El TGF-beta síntesis y mecanismo de acción / TGF-ß: synthesis and mecanism of action

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