There is a global trend toward intensive livestock breeding, which tends to increase the microbial load in the environment as well as the presence of volatile compounds and dust that can cause health issues. Cattle is the major producer of Escherichiacoli (E. coli), a group of foodborne bacteria associated with severe human diseases, and Neuquén province in Argentina has one of the highest rates of uremic hemolytic syndrome incidence in the world. This paper presents the results of two sampling events of E. coli bacteria at 39 sites in La Paisana ranch (LPR), in Añelo (Neuquén), considering locations inside the pens, upwind, and downwind of the feedlot with different time steps, using a Microflow α equipment. The ranch has approximately 600 heads and clean and controlled installations. The field experiment included sampling airborne aerosol deposition and concentration using passive and active methods. Concentrations were also estimated using an atmospheric dispersion model. During the field experiment, counts of up to 2970 CFU/m3 were obtained in the cattle stockyards and up to 111 CFU/m3 at a distance of 100 m.

Lozano, Eduardo Enrique. Universidad Nacional de Rio Negro. Centro de Estudios e Investigacion en Educacion. Rio Negro, Argentina.

Paez, Paula Andrea. Universidad Nacional de Rio Negro. Centro de Investigaciones y Transferencias de Rio Negro. Rio Negro, Argentina

El proceso de diseño, implementación y evaluación de Unidades Didácticas (UD), constituye un potente dispositivo para el desarrollo de innovaciones en la enseñanza de las ciencias y puede dar lugar a transformaciones profundas en las prácticas educativas. En el contexto de un Profesorado en Biología en el ámbito de la Universidad, las UD nos permiten concretar y especificar vinculaciones entre el campo de la formación en didáctica y el campo de la formación disciplinar en biología, y también integrar la modelización de fenómenos biológicos y de ideas clave metacientíficas, de manera sincrónica, a partir de la consideración de hechos sociocientíficos que contextualizan y dan sentido a la enseñanza. En este marco, la investigación se desarrolló desde un enfoque cualitativo, implementando “estudios de diseño” en “ciclos iterativos”, con el objetivo de diseñar, implementar y evaluar una UD en la disciplina Biología Humana, para la enseñanza del modelo de “regulación de la presión arterial” (PA), en paralelo al desarrollo de una idea clave sobre “paradigma”. En este artículo se presenta una síntesis de la UD integradora, un detalle de las actividades que colaboraron en la construcción de una idea sobre “paradigma” y el análisis de las producciones de los y las estudiantes, las que dan cuenta de un proceso significativo de reelaboración y complejización de ideas respecto de qué son y cómo operan los paradigmas en la actividad científica.

En este artículo se presentan los fundamentos teóricos y los resultados de una investigación llevada a cabo a partir del diseño, implementación y evaluación de una unidad didáctica para la modelización del fenómeno de presión arterial (PA) y su regulación, advertida desde modelos teóricos del campo de la didáctica, en la asignatura Biología Humana de un profesorado de nivel medio y superior en Biología. La unidad se estructuró a partir del abordaje de un hecho sociocientífico e integró contenidos disciplinares de la Biología, vinculados con la pa y los mecanismos para su regulación, con contenidos metacientíficos, que favorecieron la reflexión por parte de los estudiantes sobre determinados aspectos de la ciencia. Se presenta el análisis de los datos de la línea disciplinar biológica que ha dado lugar a una caracterización de los modelos iniciales de los estudiantes, de los modelos intermedios, de los de arribo y de su aplicación. El proceso de modelización llevado a cabo por los estudiantes refleja una complejización ya que, desde modelos inicialmente simples y anclados en el nivel de organización celular, fueron incorporando a partir de las actividades trabajadas, nuevas y más complejas relaciones, lo que favoreció la construcción de modelos con una visión sistémica del fenómeno de la PA y su regulación.

Las Unidades didacticas (UDs) constituyen un potente dispositivo para el desarrollo de innovaciones en la ensenanza de las ciencias. Pueden dar lugar a transformaciones profundas en las practicas educativas y tambien colaborar en la reconfiguracion de diferentes campos intervinientes en un area de formacion. Situados en el contexto del profesorado en Biologia en el ambito de la universidad, presentamos y fundamentamos tres aspectos innovadores promovidos por el diseno e implementacion de UDs: la vinculacion de los campos de la formacion disciplinar y didactica, la integracion de la modelizacion disciplinar y metacientifica y la interaccion especifica y productiva entre esas modelizaciones. Luego se presentan dos UDs, una, elaborada e implementada en una materia del eje de formacion disciplinar, y otra, en una materia del eje de formacion didactica y se identifican en ellas los aspectos mencionados. El marco teorico que orienta el trabajo de diseno de las UDsse referencia en el Modelo cognitivo de ciencia escolar, la Actividad cientifica escolar y la modelizacion, el eje Naturaleza de la ciencia y la perspectiva de Asuntos sociocientificos.

In strawberry, the putative participation of aquaporins should be considered during fruit ripening. Furthermore, the availability of different firmness cultivars in this non-climacteric fruit is a very useful tool to determine their involvement in softening. In a previous work, the cloning of a strawberry fruit-specific aquaporin, FaPIP1;1, which showed an expression profile associated with fruit ripening was reported. Here, FaPIP2;1, an aquaporin subtype of PIP2 was cloned and its functional characterization in Xenopus oocytes determined. The FaPIP2;1 gene encodes a water channel with high water permeability (Pf) that is regulated by cytosolic pH. Interestingly, the co-expression of both FaPIP subtypes resulted in an enhancement of water permeability, showing Pf values that exceeds their individual contribution. The expression pattern of both aquaporin subtypes in two cultivars with contrasting fruit firmness showed that the firmer cultivar (Camarosa) has a higher accumulation of FaPIP1 and FaPIP2 mRNAs during fruit ripening when compared with the softer cultivar (Toyonoka). In conclusion, not only FaPIP aquaporins showed an expression pattern associated with fruit firmness but it was also shown that the enhancement of water transfer through the plasma membrane is coupled to the presence/absence of the co-expression of both subtypes.

Despite the advances in the physiology of fruit ripening, the role and contribution of water pathways are still barely considered. Our aim was therefore to characterize aquaporins, proteins that render the molecular basis for putative regulatory mechanisms in water transport. We focused our work on strawberry (Fragaria xananassa) fruit, a non-climacteric fruit of special interest because of its forced brief commercial shelf life. A full-length cDNA was isolated with high homology with plasma membrane (PM) intrinsic proteins (named FaPIP1;1), showing a profile with high expression in fruit, less in ovaries and no detection at all in other parts. Its cellular localization was confirmed at the PM. As reported in other plasma membrane intrinsic proteins subtype 1 (PIP1s), when expressing the protein in Xenopus leavis oocytes, FaPIP1;1 shows low water permeability values that only increased when it is coexpressed with a plasma membrane intrinsic protein subtype 2. Northern blotting using total RNA shows that its expression increases during fruit ripening. Moreover, functional characterization of isolated PM vesicles from red stage fruit unequivocally demonstrates the presence of active water channels, i.e. high water permeability values and a low Arrhenius activation energy, both evidences of water transport mediated by proteins. Interestingly, as many ripening-related strawberry genes, the expression pattern of FaPIP1;1 was also repressed by the presence of auxins. We therefore report a fruit specific PIP1 aquaporin with an accumulation pattern tightly associated to auxins and to the ripening process that might be responsible for increasing water permeability at the level of the PM in ripe fruit.

Despite the fact that anoxic goldfish hepatocytes can maintain the transmembrane gradients of Na+, H+ and Ca2+, cyanide (CN) intoxication leads to a rapid breakdown of K+ homeostasis. In this study, [86Rb+] K+ fluxes across the plasma membrane of goldfish hepatocytes were studied in order to identify the possible causes of this imbalance. Four minutes of cyanide incubation induced an acute and stable 61% decrease of K+ influx (mostly driven by Na,K-ATPase activity), whereas K+ efflux increased by 24.3%, this imbalance yielding a net K+ efflux of 0.279 ± 0.024 nmol 10−6 cells−1 min−1. This uncoupling was not observed when glycolytic ATP production was inhibited with iodoacetic acid. Although the CN-induced decrease of K+ influx was fully reversible upon washout of the inhibitor, it could not be prevented by any of the following treatments: (1) addition of 2% bovine serum albumin, which binds extracellular fatty acids known to activate specific K+ channels; (2) addition of ascorbate, which acts as a radical scavenger; (3) inclusion of 5 mM glucose as an extracellular carbon source; and (4) removal of medium oxygen (obtained by nitrogen bubbling). Regarding the elevation of K+ efflux in the presence of CN, neither ATP-dependent K+ channels nor the KCl cotransporter appeared to be activated, whereas BaCl2, an inhibitor of voltage-gated K+ channels, decreased K+ efflux of CN-intoxicated cells to control levels. In summary, these results indicate that, in goldfish hepatocytes, the CN-induced K+ imbalance results from acute Na,K-ATPase inhibition together with the activation of voltage-dependent K+ channels, the latter probably resulting from transient membrane depolarization.

In trout hepatocytes, hypotonic swelling is followed by a compensatory shrinkage called regulatory volume decrease (RVD). It has been postulated that extracellular ATP and other nucleotides may interact with type 2 receptors (P(2)) to modulate this response. In addition, specific ectoenzymes hydrolyze ATP sequentially down to adenosine, which may bind to type 1 receptors (P(1)) and also influence RVD. Accordingly, in this study, we assessed the role of extracellular nucleoside 5'-tri- and diphosphates and of adenosine on RVD of trout hepatocytes. The extent of RVD after 40 min of maximum swelling was denoted as RVD(40), whereas the initial rate of RVD was called v(RVD). In the presence of hypotonic medium (60% of isotonic), hepatocytes swelled 1.6 times followed by v(RVD) of 1.7 min(-1) and RVD(40) of 60.2%. ATP, UTP, UDP, or ATPgammaS (P(2) agonists; 5 microM) increased v(RVD) 1.5-2 times, whereas no changes were observed in the values of RVD(40). Addition of 100 microM suramin or cibacron blue (P(2) antagonists) to the hypotonic medium produced no effect on v(RVD) but a 53-58% inhibition of RVD(40). Incubation of hepatocytes in the presence of either 5 microM [gamma-(32)P]ATP or [alpha-(32)P]ATP induced the extracellular release of [gamma-(32)P]P(i) (0.21 nmol.10(-6) cells(-1).min(-1)) and [alpha-(32)P]P(i) ( approximately 8 x 10(-3) nmol.10(-6) cells(-1).min(-1)), suggesting the presence of ectoenzymes capable of fully dephosphorylating ATP. Concerning the effect of P(1) activation on RVD, 5 microM adenosine, both in the presence and absence of 100 microM S-(4-nitrobenzil)-6-tioinosine (a blocker of adenosine uptake), decreased RVD(40) by 37-44%, whereas 8-phenyl theophylline, a P(1) antagonist, increased RVD(40) by 15%. Overall, results indicate that ATP, UTP, and UDP, acting via P(2), are important factors promoting RVD of trout hepatocytes, whereas adenosine binding to P(1) inhibits this process.

SUMMARY The relationship between cell volume and K+ transmembrane fluxes of goldfish (Carassius auratus) hepatocytes exposed to anisotonic conditions or energetic limitation was studied and compared with the response of hepatocytes from trout (Oncorhynchus mykiss) and rat (Rattus rattus). Cell volume was studied by video- and fluorescence microscopy,while K+ fluxes were assessed by measuring unidirectional 86Rb+ fluxes. In trout and rat hepatocytes, hyposmotic (180 mosmoll-1)exposure at pH 7.45 caused cell swelling followed by a regulatory volume decrease (RVD), a response reported to be mediated by net efflux of KCl and osmotically obliged water. By contrast, goldfish hepatocytes swelled but showed no RVD under these conditions. Although in goldfish hepatocytes a net(86Rb+)K+ efflux could be activated by N-ethylmaleimide, this flux was not, or only partially, activated by hyposmotic swelling (120-180 mosmoll-1). Blockage of glycolysis by iodoacetic acid (IAA) did not alter cell volume in goldfish hepatocytes, whereas in the presence of cyanide (CN-),an inhibitor of oxidative phosphorylation, or CN- plus IAA(CN-+IAA), cell volume decreased by 3-7%. Although in goldfish hepatocytes, energetic limitation had no effect on(86Rb+)K+ efflux,(86Rb+)K+ influx decreased by 57-66% in the presence of CN- and CN-+IAA but was not significantly altered by IAA alone. Intracellular K+ loss after 20 min of exposure to CN- and CN-+IAA amounted to only 3% of the total intracellular K+. Collectively, these observations suggest that goldfish hepatocytes, unlike hepatocytes of anoxia-intolerant species, avoid a decoupling of transmembrane K+ fluxes in response to an osmotic challenge. This may underlie both the inability of swollen cells to undergo RVD but also the capability of anoxic cells to maintain intracellular K+ concentrations that are almost unaltered, thereby prolonging cell survival.