Time-irreversible subconductance gating associated with Ba2+ block of large conductance Ca2+-activated K+ channels.

Ba2+ block of large conductance Ca2+-activated K+ channels was studied in patches of membrane excised from cultures of rat skeletal muscle using the patch clamp technique. Under conditions in which a blocking Ba2+ ion would dissociate to the external solution (150 mM N-methyl-D-glucamine+o, 500 mM K+i, 10 microM Ba2+i, +30 mV, and 100 microM Ca2+i to fully activate the channel), Ba2+ blocks with a mean duration of approximately 2 s occurred, on average, once every approximately 100 ms of channel open time. Of these Ba2+ blocks, 78% terminated with a single step in the current to the fully open level and 22% terminated with a transition to a subconductance level at approximately 0.26 of the fully open level (preopening) before stepping to the fully open level. Only one apparent preclosing was observed in approximately 10,000 Ba2+ blocks. Thus, the preopenings represent Ba2+-induced time-irreversible subconductance gating. The fraction of Ba2+ blocks terminating with a preopening and the duration of preopenings (exponentially distributed, mean = 0.75 ms) appeared independent of changes in [Ba2+]i or membrane potential. The fractional conductance of the preopenings increased from 0.24 at +10 mV to 0.39 at +90 mV. In contrast, the average subconductance level during normal gating in the absence of Ba2+ was independent of membrane potential, suggesting different mechanisms for preopenings and normal subconductance levels. Preopenings were also observed with 10 mM Ba2+o and no added Ba2+i. Adding K+, Rb+, or Na+ to the external solution decreased the fraction of Ba2+ blocks with preopenings, with K+ and Rb+ being more effective than Na+. These results are consistent with models in which the blocking Ba2+ ion either induces a preopening gate, and then dissociates to the external solution, or moves to a site located on the external side of the Ba2+ blocking site and acts directly as the preopening gate.

Two-dimensional components and hidden dependencies provide insight into ion channel gating mechanisms.

Correlations between the durations of adjacent open and shut intervals recorded from ion channels contain information about the underlying gating mechanism. This study presents an additional approach to extracting the correlation information. Detailed correlation information is obtained directly from single-channel data and quantified in a manner that can provide insight into the connections among the states underlying the gating. The information is obtained independently of any specific kinetic scheme, except for the general assumption of Markov gating. The durations of adjacent open and shut intervals are binned into two-dimensional (2-D) dwell-time distributions. The 2-D (joint) distributions are fitted with sums of 2-D exponential components to determine the number of 2-D components, their volumes, and their open and closed time constants. The dependency of each 2-D component is calculated by comparing its observed volume to the volume that would be expected if open and shut intervals paired independently. The estimated component dependencies are then used to suggest gating mechanisms and to provide a powerful means of examining whether proposed gating mechanisms have the correct connections among states. The sensitivity of the 2-D method can identify hidden components and dependencies that can go undetected by previous correlation methods.

High Ca2+ concentrations induce a low activity mode and reveal Ca2(+)-independent long shut intervals in BK channels from rat muscle.

1. Large-conductance calcium-activated K+ channels (BK channels) often display long closed intervals at higher levels of Ca2+. To gain further insight into possible mechanisms for these intervals, currents were recorded from single BK channels, using the patch clamp technique, from patches of membrane excised from primary cultures of rat skeletal muscle. 2. High intracellular calcium concentrations ([Ca2+]i; 10-1000 microM) induced a low activity mode and revealed isolated long shut intervals. Neither of these phenomena were due to the Ba2+ that typically contaminates reagent grade salts. 3. The low activity mode was characterized by typically single brief open intervals with mean durations of 0.1 ms, separated by long shut intervals with mean durations of 100 ms. The very low open probability of about 0.001 during the low activity mode would make a sojourn to this mode functionally equivalent to a sojourn to an inactive state. The durations of sojourns in the low activity mode were exponentially distributed, with the mean durations ranging from about 1 s in 10 microM Ca(i)2+, to 4.5 s in 1000 microM Ca(i)2+. With increased filtering, the brief open intervals would escape detection so that a sojourn to the low activity mode would appear as a single shut interval. A typical channel spent less than 5% of its time in the low activity mode for [Ca2+]i < 10 microM. This increased to about 30% for [Ca2+]i > 100-1000 microM. A kinetic model with three closed states and two open states could approximate the gating of the low activity mode. 4. The isolated long shut intervals were not from the low activity mode, suggesting a different underlying mechanism. Their frequency of occurrence of about 0.3 s-1 did not increase with increasing [Ca2+]i, indicating that they did not arise from a slow Ca2+ block. Their durations were exponentially distributed, with a mean of 127 ms, which was independent of [Ca2+]i, suggesting that a single Ca(2+)-independent closed state or block underlies the isolated long shut intervals. At higher [Ca2+]i, up to 60% of the shut time could be spent in the isolated long shut intervals. 5. These observations suggest that activation of BK channels by high [Ca2+]i can be limited by sojourns to a low activity mode and also by isolated long shut intervals, two additional phenomena that will have to be accounted for in the gating of BK channels.

[Physicochemical evaluation of dried salted fish in Venezuela]. / Evaluación físico-química del pescado seco-salado en Venezuela.

Several physical and chemical characteristics of dried salted fish obtained from Venezuelan's market were evaluated. Determinations of moisture, ash, fat, protein, pH, sodium chloride. Total Volatile Nitrogen and water activity, were performed on such products. Even though on limiting parameters, the values of water activity, moisture and NaCl determination, indicated that the fish quality was acceptable. Total Volatile Nitrogen and pH values were related more to the particular fish species. Four different fish species were salted and dried following the "optimal method", and an excellent product was obtained, without using expensive or complex methods.

[Evaluation of biological fish silage in broiler chicken]. / Evaluación del ensilado biológico de pescado en pollos de engorde.

Biological fish silage was produced from the mixture of three low price fish species. After mixing it with molasse, papaya and pineapple wastes, and Lactobacillus plantarum incoculation, the product was stored for seven days, dehydrated and added to several diets of formulated poultry feed as a substitute of fish meal. Physical-chemical and microbiological analyses were done to the raw materials and final products. Biological tests of acceptability indicated that chicken preferred diets up to 50% of fish silage. Chicken's weigh increased and food consumption tests, in addition to the sensory evaluation tests in the chickens white meat, showed the advantages of inclusion of 5-20% fish silage in the diets of experimental animals.

[Evaluation of fish silage prepared by microbiological route as a proteinic supplement in diets for fattening chickens]. / Evaluación del ensilado de pescado elaborado por vía microbiológica como suplemento proteínico en dietas para pollos de engorde.

A bioassay in broilers was carried out during a six-week period, to evaluate, as a protein source, the quality of fish silage produced by microbiological means and to compare it with that of fish flour and soybean flour. A total of 28 broilers of the Cross by Cross strain were used, sexed and assigned at random. Additionally, the fish silage was subjected to moisture (8.1%), ash (18.4%), protein (59.5%), fat (7.55%), carbohydrates (6.47%), and pH (4.2) determinations for its inclusion in the diets formulation. The results obtained did not permit establishment of significant differences between the weight increments presented by chicks fed with fish flour, and those fed with fish silage. Nevertheless, the food conversion index of the chicks consuming the diet prepared with fish silage proved to be better that the conversion index of the diet prepared with fish and soy flours. No lesions in the organs of the animals studied were observed, and the sensory trials indicated that chicks fed with the fish silage did not present differences with those commercially acquired.

Evaluación del ensilado de pescado elaborado por via microbiológica como suplemento proteínico en dietas para pollos de engorde / Evaluation of fish silage prepared by microbiological rout as proteinic supplement in diets for fattening chickens

Se llevó a cabo un bioensayo de seis semanas, con pollos de engorde, para evaluar la calidad del ensilado de pescado producido por vía microbiana como fuente proteínica, y compararlo con harina de pescado y harina de soya. Se utilizaron, para el caso, 128 pollo sexados del cruce Cobb x Cobb, dispuestos en forma aleatoria. Adicionalmente, el ensilado de pescado se sometió a determinaciones de humedad (8.1%), cenizas (18.4%), proteínas (59.5%), grasas (7.55%), carbohidratos (6.47%), pH (4.2) a fin de efectuar su inclusión en la formulación de las dietas. Los resultados obtenidos no permitieron establecer diferencias significativas entre los incremento de peso desarrollados por las aves alimentadas con harina de pescado y los pollos alimentados con ensilado de pescado. Sin embargo, el índice de conversión de la aves que consumieron la dieta con ensilado de pescado resultó ser mejor que el índice de conversión de la dieta con harina de pescado y con harina de soya. No se observaron lesiones en los órganos de las aves sometidas a estudio, y las pruebas sensoriais indicaron que los pollos alimentados con ensilado de pescado no presentaban diferencias con los pollo adquiridos comercialmente

[Fish silage prepared from fish species of shrimp by-catch. II. Biological test in broilers]. / Ensilado de pescado a partir de la fauna de acompañamiento del camarón. II. Prueba de comportamiento en pollos de engorde.

The purpose of this study was the nutritional evaluation of proteins in fish silage. A biological test was conducted in chicks (broilers) to evaluate two levels of inclusion of fish silage (2.5% and 5%, respectively) in diets normally used for feeding them. Chicks were evaluated in weight gain, food consumption, and feeding conversion index. Finally, flavor and acceptability tests of meat from broilers fed the experimental diet were conducted. Results of the biological assay indicated that the best biological response was that of the animals fed the 5% fish silage diet. Sensory tests revealed that the meat of chicks fed the experimental diets had favorable acceptance by the consumers.

[Fish silage from shrimp by catch fish: I. Preparation and biological evaluation]. / Ensilado de pescado a partir de la fauna de acompañamiento del camarón. I. Elaboración y evaluación biológica.

Fish silage was prepared from some fish species of the shrimp by-catch caught in Golfo Triste, Carabobo, Venezuela. Fish were ground until a particle size that would guarantee the liquefaction process was achieved. The process was accelerated by the incorporation of a 3.5% w/w acid mixture, formed by diluted sulfuric acid (1:3) and concentrated formic acid, in a proportion of 1:4. The silage process occurred spontaneously at room temperature during 17 days. Chemical, physical and microbiological tests were conducted in order to characterize both the raw material and the final product. The raw material used had adequate levels of freshness, so that it was suitable for use, thus producing a first-grade silage. A first biological evaluation was carried out in rats in order to estimate the protein quality of the silage by means of certain biological parameters such as PER, NPR and apparent digestibility percentage of the protein. The results of the first experimental period demonstrated that the fish silage protein was of optimal quality, since the biological response in rats was similar to that of the control group fed the casein diet.

[Preparation of a spread from shrimp by-catch fish]. / Elaboración de pasta para untar a partir de especies de pescado pertenecientes a la fauna de acompañamiento del camarón.

The composition of shrimp by-catch fish from the Central-Western region of Venezuela at different periods of the year was studied, as well as mean size and weight of same, and the yields obtained during processing, until the edible portion (pulp) was reached. The pulp was also analyzed from the physical, chemical and microbiological (pH, basic volatile N, trimethylamine, thiobarbituric acid test, moisture, fat, protein, ashes content and mesophyll and psychrophilic counts) points of view. The purpose of these studies was to determine its quality and freshness, since said pulp was utilized for the preparation of a canned and sterilized bread spread. Results obtained indicated the pulp to have an acceptable freshness, a fact which reflected in a final product with adequate characteristics. The bread spread was also analyzed from the physical, chemical, microbiological and sensory viewpoints (objective analyses of color and texture, pH, rancidity and sterility tests, moisture, fat protein, ashes, carbohydrates, sodium chloride contents, and sensory evaluation). In addition, these analyses were repeated monthly during the three-month storage period at two temperatures. On the basis of the above-mentioned findings, it was possible to determine that the bread spread had adequate acceptability and stability during storage. Furthermore, raw material variations did not affect the final product characteristics, which resulted in a product with commercial potential.

Elaboración de pasta para untar a partir de especies de pescado pertenecientes a la fauna de acompañamiento del camaron / Preparation of a bread spread from shrimp by-catch fish

Se estudió la composición de especies de pescado de la fauna de acompañamiento del camarón proveniente de la región Centro-Occidental de Venezuela en diferentes épocas del año. Asimismo, se estudió la talla y el peso promedio y los rendimientos obtenidos durante el procesamiento de las mismas, hasta la obtención de la porción comestible (pulpa). Se analizó también dicha pulpa desde el punto de vista físico, químico y microbiológico (pH, nitrógeno básico volátil, trimetilamina, prueba del ácido tiobarbitúrico, humedad, grasa, proteína, cenizas y contajes de mesófilos y psicrófilos), con el fin de determinar su calidad y frescura, ya que la misma fue utilizada para la elaboración de una pasta para untar, enlatada esterilizada. Los resultados obtenidos indican un aceptable estado de frescura de la pulpa, reflejándose esto en la obtención de un producto con características adecuadas. La pasta para untar obtenida fue analizada también desde el punto de vista físico, químico, microbiológico y sensorial (análisis objetivos de color y textura, determinación del pH, rancidez, test de esterilidad, humedad, grasa, proteína, cenizas, carbohidratos, cloruro de sodio y evaluación sensorial). Además, dichos análisis fueron repetidos mensualmente durante un período de almacenamiento de tres meses a dos temperaturas. A partir del estudio en cuestión se pudo determinar que la pasta para untar presentaba una aceptabilidad adecuada y estabilidad durante el almacenamiento. Según se observó, la variación...

[Preparation and evaluation of fish portions from shrimp by-catch]. / Elaboración y evaluación de porciones de pescado a partir de especies integrantes de la fauna de acompañamiento del camarón.

Fish portions were obtained from a mixture of fish flesh from shrimp by-catch. Physical, chemical, microbiological and sensory tests were done to evaluate quality of raw materials, formulations and processing conditions. Several technological procedures proved to be feasible for this product. Stability of frozen products for four months was determined by physical, chemical and microbiological tests, the results of which indicated its stability during the study period. Findings of our study, therefore, suggest the potential of shrimp by-catch for the preparation of fish portions in view of its high acceptability and simple processing technique, by using marine resources not fully utilized at present.

[Preparation of frozen blocks of fish flesh and its evaluation during storage]. / Elaboración de bloques congelados de pulpa de pescado y su evaluación durante el almacenamiento.

Minced fish flesh from shrimp by-catch was used as raw material to prepare four frozen blocks under different conditions, as follows: a) Minced fish flesh washed in cool water for 10 minutes with continuous stirring (water-fish proportion, 3:1). b) Minced fish flesh mixed with sodium tripolyphosphate (TPP) (0.5%), and sodium chloride (1%), respectively. c) Minced fish flesh mixed with 0.5% sodium tripolyphosphate, 1% sodium chloride and 7.5% corn starch, and c) Minced fish flesh without any treatment, which was used as control. Fish blocks were frozen at -40 degrees C and stored at -10 degrees C and -30 degrees C freezing points during a six-month period. Physical, chemical and microbiological tests were performed during the storage period. The results obtained indicate that frozen fish blocks stored at -10 degrees C deteriorate faster than those stored at -30 degrees C. The TPP, sodium chloride and corn starch treatments were not effective in reducing protein denaturation, but they do increase the water retention capacity of the blocks.

[Effect of mechanical deboning process on the fat stability of 3 tropical fish species stored at -10 degrees C]. / Efecto del proceso de deshuesado mecánico en la estabilidad de las grasas de tres especies de pescado tropicales almacenadas a -10 grados C.

Maximum advantage of certain fish species captured with shrimp, at present not fully utilized, constitutes a necessity in Venezuela. The purpose of this research work was to evaluate the stability of three of those fish species: bagre, cunaro and caballa, based on the changes that might occur in their fat content. This was done by comparing both the edible part of the whole fish, as well as the deboned flesh of each of them. Evaluation of the changes was performed by means of the acid and peroxide indices, with previous fat extraction, and the thiobarbituric acid (TBA) index. On the other hand, the fatty acids profile of the three species studied was determined by gas chromatography. According to our findings, the greater alteration was detected in the deboned sample, obtaining the highest TBA and acidity index values of all species, on the third month of storage; then a reduction of these values was observed. On the other hand, the peroxide index presented heterogeneous values in the three species analyzed through their storage period. The predominant fatty acids were: palmitic (16:0) among the saturated, and oleic (18:1) among the unsaturated. A greater proportion of unsaturated fatty acids was found in the three species. An increment of these in the deboned sample with respect to the whole fish, was also observed.

Efecto del proceso de deshuesado mecánica en la estabilidad de las grasas de tres especies de pescado tropicales almacenadas A-10-C / Effect of mechanical deboning process on the fat stability of 3 tropical fish species stored at - 10 degrees C

En Venezuela es necesario aprovechar al máximo las especies sub-utilizadas de pescado que se capturan con el camarón. Este trabajo tuvo por propósito evaluar la estabilidad de tres especies de pescados sub-utilizados: bagre, cunaro y caballa, con base en los cambios que pueden ocurrir en las grasas. Ello se hizo comparando tanto la parte comestible del pescado sin deshuesar, como la carne deshuesada de cada uno de ellos. La evaluación de los cambios se efectuó por medio de los índices de acidez y peróxido, con extración previa de la grasa y el índice del ácido tiobarbitúrico (TBA). Por otra parte, se determinó el perfil de ácidos grasos de las tres especies investigadas, valiéndose de cromatografía de gases. En todos los casos, la mayor alteración se detectó en la muestra deshuesada, obteniéndose los valores más altos, tanto de TBA como del índice de acidez en el tercer mes de almacenamiento en todas las especies; luego se notó una disminución de estos valores. Por otro parte, el índice de peróxido acusó valores heterogéneos en las tres especies analizadas a lo largo del almacenamiento. Los ácidos grasos predominantes fueron: el palmítico (16:0) entre los saturados, y el oleico (18:1) entre los insaturados. En las tres especies se constató una mayor proporción de ácidos grasos insaturados. También se observó un incremento de éstos en la muestra dehuesada con respecto al pescado sin deshuesar

Gas holdup and overall volumetric oxygen transfer coefficient in airlift contactors.

The two major types of airlift contactors, concentric-tube and external-loop, were investigated for their gas holdup (riser and downcomer) and overall mass transfer characteristics. Results obtained in batch charges of tap water and 0.15 kmol/m(3) NaCl solution are reported for external-loop airlift contactors having downcomer-to-riser cross-sectional area ratios, A(d)/A(r), ranging from 0.11

[Use of boned fish meat in the preparation of dried products]. / Utilización de la carne deshuesada de pescado en la elaboración de productos secos.

Minced fish flesh, both from Catfish (Arius sp) and from a mixture of various fish species of shrimp by-catch, were mixed with several starchy ingredients and salt. Drying at 70 degrees C was done until 4-10% moisture levels were reached. Physiochemical and microbiological tests (moisture, ash, protein, fat, pH, total volatile nitrogen, thiobarbituric tests, sodium chloride, color, total pour plate counts and yeast and mould counts) were conducted before and after drying. In addition, rehydration and sensory evaluation tests were performed in the dried products. Findings revealed that sodium chloride at 1.5% works as preservative and does not affect rehydration. Starchy ingredients favor fish particles binding and enhance sensory attributes such as color and appearance. Nevertheless, more studies in this area are recommended to reach acceptable quality products.

Utilizacion de la carne deshuesada de pescado en la elaboracion de productos secos. / Use of deboned fish meat in the preparation of dry products

La carne deshuesada, tanto de bagre (Arius sp.) como la proveniente de una mezcla de diferentes especies que conforman la fauna de acompanamiento del camaron, se mezclaron con ingredientes amilaceos y NaCl al 1,5% y 20% en base humeda. Luego se deshidrataron a 70oC, hasta alcanzar niveles de humedad del 4 al 10%. Se determinaron los indices fisico-quimicos y microbiologicos (humedad, cenizas, proteinas, grasas, pH, nitrogeno volatil total, acido tiobarbiturico, NaCl, color, contaje de bacterias, hongos y levaduras) del producto, antes y despues del secado. Adicionalmente se realizaron determinaciones de rehidratacion y evaluacion sensorial en el producto deshidratado. Segun se determino, la sal a una concentracion de 1.5% ejerce un efecto preservativo en el producto final y no afecta negativamente la rehidratacion del mismo. El agregado de ingredientes amilaceos, asimismo, favorece la union de las particulas de pescado deshuesado y mejora las caracteristicas sensoriales de color y apariencia. No obstante, se recomienda el desarrollo de estudios de esta naturaleza, con miras a lograr productos de calidad aceptable

[Feasibility of the use of different binding agents for the development of products based on deboned fish flesh]. / Factibilidad de empleo de diferentes agentes adhesivos para el desarrollo de productos a base de carne deshuesada de pescado.

Blocks of deboned fish flesh capable of developing binding, stable and adequate properties were prepared. Procedures with fish flesh and binding agents were investigated, with emphasis on the rheologic and hydration properties. Starches and precooked maize and cassava flours were used as binding agents. Flours presented a high binding capacity, even at low concentrations (10%-15%); however, at higher concentrations this property tended to be counterbalanced by the water absorption capacity. On the other hand, it was observed that application of thermal gelatinizing treatments was required when crude starch was used. As far as color is concerned, the observed changes depended both on the type of binder used and on its concentration. Findings revealed that the flesh-binding texture procedure depends on the viscosity developed by the starchy product.

Factibilidad de empleo de diferentes agentes adhesivos para el desarrollo de productos a base de carne deshuesada de pescado. / Feasibility of the use of different binding agents for the development of products based on deboned fish flesh

Se elaboraron bloques de carne deshuesada de pescado capaces de desarrollar propriedades cohesivas estables y apropiadas para el moldeo. Se investigaron sistemas preparados con carne de pescado y agentes adhesivos, haciendo enfasis en las propiedades reologicas y de hidratacion. Como agentes adhesivos se utilizaron almidones y harinas precocidas de maiz y yuca. Las harinas presentaron una alta capacidad adhesiva, aun a bajas concentraciones (10%15%); sin embargo, a concentraciones mayores esta propiedad tendio a ser antagonizada por la capacidad de absorcion de agua. Por otro lado, se observo que el empleo de almidon crudo exige la aplicacion de tratamientos termicos gelatinizantes.En cuanto a color, los cambios observados dependieron tanto del tipo de adhesivo como de su concentracion. Se encontro que la textura del sistema carne-adhesivo utilizado, depende de la viscosidad desarrollada por el producto amilaceo