Equilibrium Properties of Mouse-Torpedo Acetylcholine Receptor Hybrids Expressed in Xenopus Oocytes

This study used messenger RNA encoding each subunit (α, β, γ and δ) of the nicotinic acetylcholine (ACh) receptor from mouse BC3H-1 cells and from Torpedo electric organ. The mRNA was synthesized in vitro by transcription with SP6 polymerase from cDNA clones. All 16 possible combinations that include one mRNA for each of α, β, γ and δ were injected into oocytes. After allowing 2-8 d for translation and assembly, we assayed each oocyte for (a) receptor assembly, measured by the binding of [^125]α-bungarotoxin to the oocyte surface, and (b) ACh-induced conductance, measured under voltage clamp at various membrane potentials. All combinations yielded detectable assembly (30-fold range among different combinations) and ACh-induced conductances (>1,000-fold range at 1 µM). On double-logarithmic coordinates, the dose-response relations all had a slope near 2 for low concentrations of ACh. Data were corrected for variations in efficiency of translation among identically injected oocytes by expressing ACh-induced conductance per femtomole of α-bungarotoxin-binding sites. Five combinations were tested for d-tubocurarine inhibition by the dose-ratio method; the apparent dissociation constant ranged from 0.08 to 0.27 µM. Matched responses and geometric means are used for describing the effects of changing a particular subunit (mouse vs. Torpedo) while maintaining the identity of the other subunits. A dramatic subunit-specific effect is that of the β subunit on voltage sensitivity of the response: g_ACh(-90 mV)/g_Ach(+30 mV) is always at least 1, but this ratio increases by an average of 3.5-fold if β_M replaces β_T. Also, combinations including γ_T or δ_M usually produce greater receptor assembly than combinations including the homologous subunit from the other species. Finally, E_ACh is defined as the concentration of ACh inducing 1 µS/fmol at -60 mV; E_ACh is consistently lower for α_m. We conclude that receptor assembly, voltage sensitivity, and E_ACh are governed by different properties

When the path is never shortest: a reality check on shortest path biocomputation

Shortest path problems are a touchstone for evaluating the computing performance and functional range of novel computing substrates. Much has been published in recent years regarding the use of biocomputers to solve minimal path problems such as route optimisation and labyrinth navigation, but their outputs are typically difficult to reproduce and somewhat abstract in nature, suggesting that both experimental design and analysis in the field require standardising. This chapter details laboratory experimental data which probe the path finding process in two single-celled protistic model organisms, Physarum polycephalum and Paramecium caudatum, comprising a shortest path problem and labyrinth navigation, respectively. The results presented illustrate several of the key difficulties that are encountered in categorising biological behaviours in the language of computing, including biological variability, non-halting operations and adverse reactions to experimental stimuli. It is concluded that neither organism examined are able to efficiently or reproducibly solve shortest path problems in the specific experimental conditions that were tested. Data presented are contextualised with biological theory and design principles for maximising the usefulness of experimental biocomputer prototypes.Comment: To appear in: Adamatzky, A (Ed.) Shortest path solvers. From software to wetware. Springer, 201

Arzner, Dorothy (1897–1979)

Dorothy Arzner was the only American woman that was successful in both the silent and the sound era. She was the only woman director working for Hollywood in the 1930s and one of the very few female Hollywood directors that have been successful from the 1920s to the 1940s. Arzner in fact came to symbolize everything that women could achieve in cinema and her work had a great influence on later women directors such as Ida Lupino, Joan Micklin Silver, and Elaine May. Her films were reclaimed by feminist scholars during the 1970s as texts that subvert patriarchal constructions of gender. In particular, feminist film critics often quote Arzner\u27s Dance, Girl, Dance (1940) as a film that actively critiques the culture of the spectacle where the woman is objectified by the gaze of the camera. Overall, although Arzner uses the “master\u27s tools,” she still manages to dismantle “the master\u27s house” by denaturalizing the gender conventions of her era

Diet, Obesity and Reflux in the Etiology of Adenocarcinomas of the Esophagus and Gastric Cardia in Humans

Incidence rates for esophageal adenocarcinoma have increased \u3e350% since the mid-1970s. Rates for gastric cardia adenocarcinoma have also increased, although less steeply. This led to the initiation of large population-based case-control studies, particularly in the United States and Sweden, aimed at identifying risk factors for these cancers. Results have been emerging from these studies, with the consistent finding that obesity and gastroesophageal reflux disease are important risk factors for these cancers. Analyses of dietary factors are also available and indicate that diets high in total fat, saturated fat and cholesterol are associated with an increased risk of these cancers, whereas several nutrients, particularly those found in plant foods (fiber, vitamin C, β-carotene, folate), are associated with a reduced risk. Considering the incidence trends of these cancers and the trends in the prevalence of risk factors, the increasing prevalence of obesity in the United States likely accounts for some of the increased incidence. However, other contributors to the increasing trends have been suggested and will be discussed. Because diet, obesity and gastroesophageal reflux disease may not act independently in contributing to these cancers, current research is attempting to identify associations between the three risk factors and potential mechanisms of action to better understand the etiology of these cancers

Development and application of the GIM code for the Cyber 203 computer

The GIM computer code for fluid dynamics research was developed. Enhancement of the computer code, implicit algorithm development, turbulence model implementation, chemistry model development, interactive input module coding and wing/body flowfield computation are described. The GIM quasi-parabolic code development was completed, and the code used to compute a number of example cases. Turbulence models, algebraic and differential equations, were added to the basic viscous code. An equilibrium reacting chemistry model and implicit finite difference scheme were also added. Development was completed on the interactive module for generating the input data for GIM. Solutions for inviscid hypersonic flow over a wing/body configuration are also presented

Cellular automata modelling of slime mould actin network signalling

© 2016, The Author(s). Actin is a cytoskeletal protein which forms dense, highly interconnected networks within eukaryotic cells. A growing body of evidence suggests that actin-mediated intra- and extracellular signalling is instrumental in facilitating organism-level emergent behaviour patterns which, crucially, may be characterised as natural expressions of computation. We use excitable cellular automata modelling to simulate signal transmission through cell arrays whose topology was extracted from images of Watershed transformation-derived actin network reconstructions; the actin networks sampled were from laboratory experimental observations of a model organism, slime mould Physarum polycephalum. Our results indicate that actin networks support directional transmission of generalised energetic phenomena, the amplification and trans-network speed of which of which is proportional to network density (whose primary determinant is the anatomical location of the network sampled). Furthermore, this model also suggests the ability of such networks for supporting signal-signal interactions which may be characterised as Boolean logical operations, thus indicating that a cell’s actin network may function as a nanoscale data transmission and processing network. We conclude by discussing the role of the cytoskeleton in facilitating intracellular computing, how computation can be implemented in such a network and practical considerations for designing ‘useful’ actin circuitry