Ca2+ waves in astrocytes.

The glial cell is the most numerous cell type in the central nervous system and is believed to play an important role in guiding brain development and in supporting adult brain function. One type of glial cell, the astrocyte also may be an integral computational element in the brain since it undergoes neurotransmitter-triggered signalling. Here we review the role of the astrocyte in the central nervous system, emphasizing receptor-mediated Ca2+ physiology. One focus is the recent discovery that the neurotransmitter glutamate induces a variety of intracellular Ca2+ changes in astrocytes. Simple Ca2+ spikes or intracellular Ca2+ oscillations often appear spatially uniform. However, in many instances, the Ca2+ rise has a significant spatial dimension, beginning in one part of the cell it spreads through the rest of the cell in the form of a wave. With high enough agonist concentration an astrocyte syncitium supports intercellular waves which propagate from cell to cell over relatively long distances. We present results of experiments using more specific pharmacological glutamate receptor agonists. In addition to describing the intercellular Ca2+ wave we present evidence for another form of intercellular signalling. Some possible functions of a long-range glial signalling system are also discussed.     

Cultures of bovine tracheal epithelium with differentiated ultrastructure and ion transport

Summary Tracheal epithelial cells were grown on Nuclepore filters coated with human placental collagen. When grown immersed in medium containing fetal bovine serum, cells displayed an undifferentiated ultrastructure (no cilia and a cell height of ∼ 10 μm). Short-circuit current (I_sc) was approximately 1/10 that of the native epithelium. By contrast, when grown in hormonally defined, serum-free medium with an air interface, cells showed I_sc equal to or greater than the original tissue, possessed cilia, and had a cell height of ∼ 50 μm. Responses in I_sc to mediators were similar to those of the original tissue, but differed from those of dog or human tracheal epithelium. Given the ready availability and low cost of the native tissues, bovine tracheal cultures grown in serum-free medium with an air interface should prove useful in studies of airway epithelial physiology.     

Ouabain-insensitive salt and water movements in duck red cells. II. Norepinephrine stimulation of sodium plus potassium cotransport

Catecholamines induce net salt and water movements in duck red cells incubated in isotonic solutions. The rate of this response is approximately three times greater than a comparable effect observed in 400 mosmol hypertonic solutions in the absence of hormone (W.F. Schmidt and T. J. McManus. 1977 a.J. Gen. Physiol. 70:59-79. Otherwise, these two systems share a great many similarities. In both cases, net water and salt movements have a marked dependence on external cation concentrations, are sensitive to furosemide and insensitive to ouabain, and allow the substitution of rubidium for external potassium. In the presence of ouabain, but the absence of external potassium (or rubidium), a furosemide-sensitive net extrusion of sodium against a large electrochemical gradient can be demonstrated. When norepinephrine-treated cells are incubated with ouabain and sufficient external sodium, the furosemide-sensitive, unidirectional influxes of both sodium and rubidium are half- maximally saturated at similar rubidium concentrations; with saturating external rubidium, the same fluxes are half-maximal at comparable levels of external sodium. In the absence of sodium, a catecholamine-stimulated, furosemide-sensitive influx of rubidium persists. In the absence of rubidium, a similar but smaller component of sodium influx can be seen. We interpret these results in terms of a cotransport model for sodium plus potassium which is activated by hypertonicity or norepinephrine. When either ion is absent from the incubation medium, the system promotes an exchange-diffusion type of movement of the co-ion into the cells. In the absence of external potassium, net movement of potassium out of the cell leads to a coupled extrusion of sodium against its electrochemical gradient.     

Comment to “Marginal and non-marginal approaches in characterization: how context and scale affect the selection of an adequate characterization factor. The AWARE model example”

The International Journal of Life Cycle Assessment -     

Obsolescence in LCA–methodological challenges and solution approaches

Purpose

Obsolescence, as premature end of use, increases the overall number of products produced and consumed, and thereby can increase the environmental impact. Measures to decrease the effects of obsolescence by altering the product or service design have the potential to increase use time (defined as the realized active service life) of devices, but can themselves have (environmental) drawbacks, for example, because the amount of material required for production increases. As such, paying special attention to methodological choices when assessing such measures and strategies using life cycle assessment (LCA) needs is crucial.

Methods

Open questions and key aspects of obsolescence, including the analysis of its effects and preventative measures, are discussed against the backdrop of the principles and framework for LCA given in ISO 14040/44, which includes guidance on how to define a useful functional unit and reference flow in the context of real-life use time.

Results and discussion

The open and foundational requirements of ISO 14040/14044 already form an excellent basis for analysis of the phenomenon obsolescence and its environmental impact in product comparisons. However, any analysis presumes clear definition of the goal and scope phase with special attention paid to aspects relevant to obsolescence: the target product and user group needs to be placed into context with the analysed “anti-obsolescence” measures. The reference flow needs to reflect a realized use time (and not solely a technical lifetime when not relevant for the product under study). System boundaries and types of data need to be chosen also in context of the anti-obsolescence measure to include, for example, the production of spare parts to reflect repairable design and/or manufacturer-specific yields to reflect high-quality manufacturing.

Conclusions

Understanding the relevant obsolescence conditions for the product system under study and how these may differ across the market segment or user types is crucial for a fair and useful comparison and the evaluation of anti-obsolescence measures.

     

The product environmental footprint communication at the crossroad: integration into or co-existence with the European Ecolabel?

The International Journal of Life Cycle Assessment - Since 2013, the European Commission (EC) is developing and testing the Product Environmental Footprint (PEF)—a product evaluation method,...     

Preface—a new paradigm for life cycle thinking: exploring sustainability in urban development scenarios

The International Journal of Life Cycle Assessment - The main goal of this special issue is to further the understanding of how to integrate life cycle sustainability assessment (LCSA) methods and...     

An environmental assessment of small hydropower in India: the real costs of dams’ construction under a life cycle perspective

The International Journal of Life Cycle Assessment - In the last years, India has taken a number of initiatives to boost small hydropower development based on the assumption of being a green energy...     

Development of Eco-factors for the European Union based on the Ecological Scarcity Method

The International Journal of Life Cycle Assessment - Weighting as an optional step in life cycle impact assessment (LCIA) has recently gained momentum through increased policy requirements in the...