Effects of disassembly of actin microfllaments on the AVP-induced regulation of sodium channel densities in frog skin epithelium

Vasopressin (AVP) stimulates the absorption of Na⁺ across frog skin epithelium by increasing the number of open apical channels (N_o) mainly through a large expansion of the total number of channels (N_T) at the membrane. This study investigates with blocker-induced noise analysis the potential role of actin in the regulation of AVP-induced changes in channel densities. Particularly we examined the idea that actin regulates the insertion of channels into apical cell membranes, consistent with the model for its hydrosmotic action. Treating cells with cytochalasin B (CB) for 2 h to disassemble the prominent subapical actin network did not significantly alter the stimulation of the I_sc by AVP. Importantly, the treatment had no significant effect on the AVP-induced activation of Na⁺ channels, nor on the increases in N_T indicating that an intact actin network is not required for the natriferic actions on the channels. This result is disparate from well known effects of CB on the AVP-induced hydrosmotic response and we assume that these distinct responses are produced by different mechanisms. Other mechanisms need to be considered to explain the mechanism whereby new Na⁺ channels are recruited to the apical membrane. In particular, mechanisms of intracellular trafficking involved in the redistribution of epithelial Na⁺ channels remain unresolved and need to be refined.     

Accuracy of RBE: experimental and theoretical considerations

The concept of the relative biological effectiveness (RBE) is essential for treatment planning in carbon ion therapy and for understanding the biological effects of high-LET radiation. As this quantity depends on many factors, both its experimental determination and the assessment of its uncertainty are not trivial. For the limiting case of zero dose, where the RBE takes its maximum value RBE_α, we present in this article a simple empirical-based approach to estimate its uncertainty. A Gaussian error calculus is applied to equally take into account both uncertainties from experiments with high- and low-LET radiation. From a theoretical point of view, we then infer, using a simple Monte Carlo model, the distribution of RBE_α values. This illustrates why the conventional error propagation approach is inappropriate in some cases. In these cases, likewise also the error estimates have to be obtained with a more sophisticated approach. Uncertainties of RBE, visualized by error bars, are of importance for treatment planning and also for setting up a precision goal for predicting biophysical models such as the local effect model.     

Relationship between saturation deficit and the survival and locomotory activity of surface dwelling Collembola

The springtails Tomocerus minor, Orchesella cincta and Isotoma viridis survive only in air with a saturation deficit near zero. Their survival time is inversely related to saturation deficit and not simply to the relative humidity. The different species show different reactions to the same saturation deficit values, which agree with the humidity preferences of the species in their natural habitats.Drought stimulates Collembola to start locomotory activity which may lead them to aggregate in optimal humidity conditions. Thus this reaction may play a part in increasing the survival rate of these animals.

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Zusammenfassung Die Beziehung zwischen Sättigungsdefizit (S.D.) und Überlebenszeit und zwischen S.D. und lokomotorischer Aktivität wurde an drei epedaphischen Collembolen-Arten untersucht. Die Überlebensdauer verhält sich umgekehrt proportional zum S.D., und steht in keinem direkten Verhältnis zur relativen Luftfeuchte. Die verschiedenen Arten weisen unterschiedliche Reaktionen zu den gleichen S.D.-Werten auf. Diese Reaktionen stimmen mit den Feuchte-Präferenzen der drei Arten in ihren natürlichen Habitats überein. Hohe S.D.-Werte führen zu lokomotorischer Aktivität, mittels welcher die Tiere optimale Feuchtigkeitsverhältnisse erreichen können.Diese Ergebnisse weisen auf einen ökologischen Überlebensmechanismus hin.

     

Mitochondrial Potentiation Ameliorates Age-Related Heterogeneity in Hematopoietic Stem Cell Function

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Expression of a rice chitinase gene in transgenic banana (��Gros Michel��, AAA genome group) confers resistance to black leaf streak disease

Transgenic banana (Musa acuminata ??Gros Michel??) integrating either of two rice chitinase genes was generated and its resistance to Black Leaf Streak disease caused by the fungus Mycosphaerella fijiensis was tested using a leaf disk bioassay. PCR screening indicated the presence of the hpt selectable marker gene in more than 90 % of the lines tested, whereas more than three quarters of the lines contained the linked rice chitinase gene resulting in a co-transformation frequency of at least 71.4 %. Further, a unique stable integration of the transgenes in each line revealed some false negative PCR results and the expected co-transformation frequency of 100 %. The transgene insert number per line ranged from 1 to 5 and single transgene insert lines (25 % of all) were identified. Considerable delay in disease development (up to 63 days post-incoculation) over a monitoring period of 108 days occurred in nine lines with extracellularly targeted chitinase out of 17 transgenic lines tested and their necrotic leaf area decreased by 73?C94 % compared to the untransformed susceptible control line. Finally, correlation between symptom development and rice chitinase expression was confirmed in two lines by Western analysis. The potential of rice chitinase genes to enhance resistance against M. fijiensis in banana was demonstrated as well as the usefulness of the leaf disk bioassay for early disease screening in transgenic banana lines.     

Activity-stimulating phenomena caused by field-disturbance in the use of pitfall-traps

Summary The influence of several mechanical field disturbances, when using pitfall-traps for activity determinations, is analysed. The disturbances result in higher catches of surface-dwelling Collembola; the animals being stimulated to higher locomotory activity.The disturbance by walking in the field results in a multiple of the control catch. This effect lasts for about 1 hour.The digging-in effect lasts for about two days but more or less different for the various species. The cause is sought in the CO₂ production in the soil, which is considerable after soil disturbances. The reaction of Collembola to rather high CO₂ concentrations in the air results in an increase of the locomotory activity.Another interpretation, namely attraction to CO₂ sources, could not be demonstrated.

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Zusammenfassung Der Einfluß verschiedener mechanischer Störungen im Feld bei der Anwendung der Fallenfangmethode wurde analysiert. Die Störungen stimulieren die Tiere zu größerer lokomotorischer Aktivität, wodurch sich höhere Fangtotale von epedaphischen Collembolen ergeben.Die Störung, welche durch vielfältiges Herumlaufen im Fangterrain entsteht, ergibt Fangtotale, die um ein Vielfaches höher sind als die Kontrollfänge. Dieser Effekt hält eine Stunde an.Eine andere Störung entsteht durch das Eingraben der Fallen. Es resultiert ebenfalls in eine höhere Anzahl gefangener Tiere. Dieser Effekt aber dauert etwa zwei Tage. Die Ursache liegt vermutlich in der Zunahme der CO₂-Produktion im Boden als Folge des Eingrabens. Erhöhte CO₂-Konzentration in der Luft resultiert tatsächlich in einer Zunahme der lokomotorischen Aktivität.Attraktion durch die CO₂-Quelle konnte nicht nachgewiesen werden.