Biomedical subjects

D B Layzell

Publications and source records attributed to D B Layzell.

3 recordsLinked to original sources

PubMed2000

A simplified approach for modeling diffusion into cells.

Regulation of the intracellular concentration of substrates is essential for the maintenance of a stable cellular environment. Diffusion and reaction processes supply and consume substrates within cells and determine their steady-state concentrations. To realistically represent these processes by computer simulation they must be modeled in three dimensions. Yet three-dimensional models are inherently computing intensive. This study describes a method, which substantially simplifies the modeling of diffusion into a polyhedral body (a cube), that was used as a model representation of a cell. The method is applied to a case study of oxygen diffusion into nitrogen-fixing, rhizobia-infected cells in legume nodules. The method involved generating a one-dimensional representation of the three-dimensional problem to provide a "surface area profile" of three-dimensional diffusion. The one-dimensional models were significantly easier to program, several orders of magnitude faster to solve and in this study were validated by assessing their results against those of comparable three-dimensional models of diffusion into the same body. The results show the one-dimensional method to be a close approximation of a three-dimensional source-sink problem with systematic differences below 10% for fractional oxygenation of leghemoglobin, cell respiration and nitrogenase activity. Larger differences between models (up to 45%) in the predicted average and innermost O(2)concentrations had no effects on the physiological conclusions of the study, but were attributed to the poorer resolution of the three- than the one-dimensional model, and to an inherent simplification in the derivation of the one-dimensional surface area profiles. The one-dimensional modeling approach was found to be a simple, yet powerful tool for the study of diffusion and reaction in biological systems.

Cell Membrane Permeability↗

PubMed2000

Oxygen regulation of a nodule-located carbonic anhydrase in alfalfa.

Control of the permeability to oxygen is critical for the function of symbiotic nitrogen fixation in legume nodules. The inner cortex (IC) seems to be a primary site for this regulation. In alfalfa (Medicago sativa) nodules, expression of the Msca1 gene encoding a carbonic anhydrase (CA) was previously found to be restricted to the IC. We have now raised antibodies against recombinant Msca1 protein and used them, together with antibodies raised against potato leaf CA, to demonstrate the presence of two forms of CA in mature nodules. Each antibody recognizes a different CA isoform in nodule tissues. Immunolocalization revealed that leaf-related CAs were localized primarily in the nitrogen-fixing zone, whereas the Msca1 protein was restricted exclusively to the IC region, in indeterminate and determinate nodules. In alfalfa nodules grown at various O(2) concentrations, an inverse correlation was observed between the external oxygen pressure and Msca1 protein content in the IC, the site of the putative diffusion barrier. Thus Msca1 is a molecular target of physiological processes occurring in the IC cells involved in gas exchange in the nodule.

Blotting, Western↗

PubMed1997

The simultaneous measurement of low rates of CO2 and O2 exchange in biological systems.

An instrument for measuring low rates of biological O2 exchange using an open-flow gas analysis system is described. A novel differential O2 sensor that is capable of measuring as little as 0.4 Pa O2 against a back-ground of ambient air (20,900 Pa O2), yet has a dynamic range of +/- 2000 Pa O2 (i.e., +/- ca. 2% O2) is described. Baseline drift was typically less than 0.025 Pa min-1. The differential O2 sensor was incorporated into a respiratory quotient/photosynthetic quotient analyzer that contained other environmental sensors for atmospheric pressure, absolute O2 and CO2 concentration, temperature of the differential O2 sensor block, and differential pressure between reference and sample streams. Protocols for how these sensors can be used to calibrate the differential O2 sensor and to improve its stability with time are described. Together, the differential O2 sensor, the environmental sensors, and the simple calibration techniques allow for simultaneous, noninvasive, and accurate measurements of O2 and CO2 exchange in tissues with metabolic rates as low as about 0.1 mumol O2 or CO2 h-1. Example data are provided in which O2 differentials of 3 to 41 Pa O2 were measured in an open-flow system.

Animals↗