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David Lewis

Publications and source records attributed to David Lewis.

42 records · Page 3Linked to original sources
PubMed2002

The slippage of the Ca2+ pump and its control by anions and curcumin in skeletal and cardiac sarcoplasmic reticulum.

Ca(2+) transport by sarcoplasmic reticulum (SR) ATPase occurs with an optimal coupling ratio of 2 Ca(2+) per ATP in pre-steady state. However, slippage of the pump and lower coupling ratios are observed in steady state. Slippage depends on the presence of high Ca(2+) in the lumen of SR vesicles and high nucleotide in the medium. Thereby, Ca(2+) and/or nucleotide-bound phosphoenzyme intermediates accumulate and undergo uncoupled cleavage, before vectorial translocation of bound Ca(2+) in the forward direction of the cycle or before productive reversal to ATP synthesis. Transport efficiency and coupling ratios are improved by reduction of nucleotide concentration in the presence of ATP regenerating systems and/or complexation of luminal Ca(2+) with phosphate or oxalate. Curcumin (1-5 microm) lowers the concentration of phosphate or oxalate required to reduce slippage of the Ca(2+) pump. Thereby, under appropriate conditions, curcumin favors kinetic flow, completion of productive cycles, and improvement of coupling ratios. The findings obtained with isolated SR vesicles suggest that slippage is an important phenomenon under prevailing conditions of muscle fibers in situ. Ca(2+) transport and its slippage can be improved by curcumin in cardiac as well as in skeletal SR, raising the possibility of pharmacological interventions to correct defective Ca(2+) homeostasis. Higher curcumin concentrations (5-30 microm), however, inhibit overall ATPase activity and Ca(2+) transport by interfering with phosphoenzyme formation with ATP or P(i).

Adenosine Diphosphate↗
PubMed2002

Cooperative setting for long-range linkage of Ca(2+) binding and ATP synthesis in the Ca(2+) ATPase.

High-affinity and cooperative binding of two Ca(2+) per ATPase (SERCA) occurs within the membrane-bound region of the enzyme. Direct measurements of binding at various Ca(2+) concentrations demonstrate that site-directed mutations within this region interfere selectively with Ca(2+) occupancy of either one or both binding sites and with the cooperative character of the binding isotherms. A transition associated with high affinity and cooperative binding of the second Ca(2+) and the engagement of N796 and E309 are both required to form a phosphoenzyme intermediate with ATP in the forward direction of the cycle and also to form ATP from phosphoenzyme intermediate and ADP in the reverse direction of the cycle. This transition, defined by equilibrium and kinetic characterization of the partial reactions of the enzyme cycle, extends from transmembrane helices to the catalytic site through a long-range linkage and is the mechanistic device for interconversion of binding and phosphorylation potentials.

Adenosine Diphosphate↗
PubMed2002

Local and interregional economic analysis of large US Department of Energy waste management projects.

An economic simulation model was used to understand the local and interregional economic impacts of four alternative waste management technologies proposed for the US Department of Energy's Savannah River nuclear weapons site. The simulations of the four technologies, each of which will cost at least a billion dollars, were done for the period 2000-2015. The analyses show that differences in project costs are not directly reflected in local economic impacts because of differences among the technologies during the design, testing and construction phases; differences in locations where the design and pilot-testing would occur; and choices about how any of the technologies would be funded.

Costs and Cost Analysis↗
PubMed2001

[Good cell culture practice (GCCP)--an initiative for standardization and quality control of in vitro studies. The establishment of an ECVAM Task Force on GCCP].

Cultured human and animal cells are increasingly used as the basis for simplified, direct test systems that have the potential to be more controllable and more reproducible than in vivo test systems. However, if a biological test system is simplified to fundamental levels then it is paramount that the essential components of such a reduced systems are closely defined and reproducible. Thus, minimal requirements for quality standards in cell and tissue culture have to be defined. It is the aim of this GCCP initiative to establish principles for standardisation, rationalisation, and international harmonisation of cell and tissue culture laboratory practices. Therefore, in analogy to Good Laboratory Practice (GLP), a Good Cell Culture Practice (GCCP) was initiated at the 3rd World Congress on Alternatives and Animal Use in the Life Sciences, Bologna, 29. August-2. September 1999. This "Bologna Statement on Good Cell Culture Practice" was presented, discussed, and refined in a Workshop, and a final version was approved at the closing ceremony of the Congress by the scientific audience. Based on the Bologna Statement, an ECVAM Task Force on GCCP was initiated, that is chaired by Thomas Hartung and Sandra Ceocke, in which experts in the field should elaborate minimal requirements for quality standards in cell culture. It is the intention of the GCCP Guidelines to encourage consensus among all concerned with the use of in vitro systems, in order to establish and maintain best laboratory practices, to promote effective quality control systems, to facilitate education and training, to support journal editors, and to help any authorities who need to interpret and apply conclusions based on in vitro data.

Animal Testing Alternatives↗
PubMedDate not supplied

Use of hyperbaric oxygen to enhance auricular composite graft survival in the rabbit model.

OBJECTIVE: To evaluate the efficacy of using hyperbaric oxygen to enhance auricular composite graft survival via a prospective, randomized, placebo-controlled, double-blind study. DESIGN: Eighteen New Zealand White rabbits were randomly assigned to treatment (n = 9) and control (n = 9) groups after amputation and reattachment of 20 x 10-mm auricular composite grafts. The treatment group received twice-daily hyperbaric oxygen treatments for 5 days. The control group received twice-daily hyperbaric room-air treatments for 5 days. After 21 days, digital photographs of the composite grafts were taken and compared with photographs taken on the day of surgery. From these photographs, digital imaging software was used to calculate the percentage of graft survival. RESULTS: The treated group (18 ears) had a mean +/- SD graft survival area of 80.67% +/- 19%, whereas the control group (18 ears) had a mean +/- SD graft survival area of 26.33% +/- 29%. Variance analysis with the Snedecor test allowed the comparison of the groups. The paired, 2-tailed t test proved a significant difference (P<.001) between groups. CONCLUSION: Hyperbaric oxygen therapy is an effective way to enhance the survival of 2-cm auricular composite grafts.

Animals↗