Search PubMed⌕ Search

Biomedical subjects

J C Weaver

Publications and source records attributed to J C Weaver.

At least 19 recordsLinked to original sources
PubMed1992

Estimates for ELF effects: noise-based thresholds and the number of experimental conditions required for empirical searches.

Interactions between physical fields and biological systems present difficult conceptual problems. Complete biological systems, even isolated cells, are exceedingly complex. This argues against the pursuit of theoretical models, with the possible consequence that only experimental studies should be considered. In contrast, electromagnetic fields are well understood. Further, some subsystems of cells (viz. cell membranes) can be reasonably represented by physical models. This argues for the pursuit of theoretical models which quantitatively describe interactions of electromagnetic fields with that subsystem. Here we consider the hypothesis that electric fields, not magnetic fields, are the source of interactions, From this it follows that the cell membrane is a relevant subsystem, as the membrane is much more resistive than the intra- or extracellular regions. A general class of interactions is considered: electroconformational changes associated with the membrane. Expected results of such as approach include the dependence of the interaction on key parameters (e.g., cell size, field magnitude, frequency, and exposure time), constraints on threshold exposure conditions, and insight into how experiments might be designed. Further, because it is well established that strong and moderate electric fields interact significantly with cells, estimates of the extrapolated interaction for weaker fields can be sought. By employing signal-to-noise (S/N) ratio criteria, theoretical models can also be used to estimate threshold magnitudes. These estimates are particularly relevant to in vitro conditions, for which most biologically generated background fields are absent. Finally, we argue that if theoretical model predictions are unavailable to guide the selection of experimental conditions, an overwhelmingly large number of different conditions will be needed to find, establish, and characterize bioelectromagnetic effects in an empirical search. This is contrasted with well-established chemical dosimetry, which is much simpler. Because of the large number of possible electromagnetic field conditions, we also conclude that in vitro studies, rather than in vivo studies, should be emphasized in studies aimed at discovering and characterizing mechanisms for bioelectromagnetic effects.

Cell Membrane↗
PubMed1992

Radiographic anatomy of soft tissue attachments in the equine metacarpophalangeal and proximal phalangeal region.

The sites of bony attachment of the tendons, ligaments, and fibrous portion of the joint capsules of the equine metacarpophalangeal (fetlock) joint region were determined by gross dissection. These sites were transposed to standard radiographic views of the fetlock joint to yield illustrations that can be used as an aid in the diagnosis of soft tissue pathology from radiographs. Evidence of direct attachment of the common digital extensor tendon to the proximal phalanx was not found. Branches of the superficial digital flexor tendon were found to insert only on the middle phalanx. The recently described sites of insertion of the branches of the superficial digital flexor tendon to the proximal phalanx were found to be sites for attachment of the deep axial palmar ligaments of the proximal interphalangeal joint.

Animals↗
PubMed1991

Rapid clonal growth measurements at the single-cell level: gel microdroplets and flow cytometry.

We describe a new, general method for rapidly measuring clonal growth of large numbers of individual members of a cell population. This method is based on microculture of individual colony-forming units in gel microdrops (GMDs; here agarose; 20 to 90 mu in diameter), which are sufficiently robust to be handled much like cells, and diffusionally transparent for molecules of interest. Flow cytometry provides rapid measurements of GMD-entrapped microcolonies, and permits subpopulation analysis. Here the method is demonstrated with mammalian, fungal and bacterial species. Additional results illustrate rapid determination of a drug-resistant subpopulation in a mixed species sample, and nutrient sensitivity for a murine hybridoma.

Animals↗
PubMed1990

The response of living cells to very weak electric fields: the thermal noise limit.

A physical model in which cells are considered as possible detectors of very weak periodic electric fields yields a general relation between cell size and both thermally induced fluctuations in membrane potential and the maximum change in membrane potential caused by an applied field. The simplest version of the model provides a broad-band estimate of the smallest applied electric field to which membrane macromolecules can directly respond (about 10(-3) volt per centimeter). Much smaller fields (10(-6) volt per centimeter) can be detected if there is a response in only a narrow band of frequencies or if signal averaging occurs through field-induced variation in the catalytic activity of membrane-associated enzymes. Both extensions of the simplest version remove the apparent violation of the thermal noise limit found in some experiments.

Cell Physiological Phenomena↗
PubMed1990

Sampling: a critical problem in biosensing.

Biosensing is widely recognised to be of potentially major importance to medicine and related fields, but in spite of a large number of impressive and important advances, widespread practical application has lagged. We examine the thesis that 'sampling' is a process which involves all of the phenomena which are associated with the transport of analyte molecules to the active sensor site, and that problems associated with this process are now the limiting factor in further use of many existing biosensors. We conclude that an integrated process of sampling and sensing should be emphasised in developing new biosensing systems, and propose several new approaches.

Biological Transport↗
PubMed1990

Gel microdroplets and flow cytometry: rapid determination of antibody secretion by individual cells within a cell population.

We report a new method capable of rapidly determining the secretion of biologically important macromolecules from each of many individual cells within a large population. This method combines flow cytometry with gel microdroplets (GMDs), which in this study were agarose particles ranging from about 53 to 88 mu in diameter. The GMDs were formed from a liquid 2.5% agarose suspension with cells at a concentration which yielded mostly zero or one cell per GMD. A large number of extracellular binding sites were also provided within each GMD, allowing the capture of secreted molecules, and their subsequent measurement by solid phase, fluorescence immunoassay. The method was explored using a model system of mouse hybridoma (secreting) and mouse masticytoma (non-secreting) cells. The method was able to determine subpopulations of individual cells that secreted antibody in less than fifteen hours after receipt of a conventional cell suspension.

Animals↗
PubMed1990

Rapid microbial detection and enumeration using gel microdroplets and colorimetric or fluorescence indicator systems.

A new micromethod employing gel microdroplets (GMDs) and optical measurements can be used for rapid detection and enumeration of viable microorganisms (J. C. Weaver, G. B. Williams, A. M. Klibanov, and A. L. Demain, Bio/Technology 6:1084-1089, 1988) and has several potential applications in clinical microbiology. This method involves entrapping microorganisms in GMDs (10 to 100 microns in diameter) which are surrounded by a hydrophobic (low dielectric) fluid, subsequently distinguishing occupied and unoccupied GMDs with colorimetric or fluorescence indicators, counting both occupied and unoccupied GMDs, and applying Poisson statistical analysis. Acid-producing microorganisms were used to compare colorimetric and fluorescence pH indicator systems. Fluorescence systems were generally superior, particularly for detection before microbial growth occurred. Although colorimetric detection was reasonably fast for fast-growing microorganisms, significantly longer times were needed for slow-growing microorganisms. We investigated the dependence of the detection time on microbial division time, GMD size, and buffering capacity of the medium within GMDs. It was found possible to use a single preparation of GMDs, containing a range of GMD sizes, to simultaneously provide a viable enumeration of growing and nongrowing (e.g., stressed) cells. This was possible because small GMDs responded rapidly to both growing and nongrowing cells, while large GMDs, although slower, responded much more rapidly to growing cells than to nongrowing cells. Separate analysis of small and large GMDs in the same preparation yielded two enumerations, one of nongrowing cells and the other of growing cells. GMDs can also be used with conventional light microscopy to detect and enumerate fast-growing acid-producing bacteria much more quickly than conventional plating methods.

Bacteria↗
PubMed1989

The number of molecules taken up by electroporated cells: quantitative determination.

Fluorescent and fluorescent-labeled molecules were used with calibrated flow cytometric fluorescence measurements of electrically pulsed cells (intact yeast: Saccharomyces cerevisiae) to demonstrate a method for determining the net number of molecules transported into electroporated cells. For the conditions used, a single pulse of width 50 microseconds and magnitude 8.0 +/- 0.5 kV/cm resulted in an average net molecular uptake which is large, n = 1.4 x 10(5) molecules of 70 kDa FITC-dextran (supplied extracellular concentration of 500 microM), and n = 1.0 x 10(8) molecules of 660 Da propidium iodide (PI; 80 microM). Both molecules were present in pulsed cells at less than equilibrium values, consistent with a transient uptake mechanism. Intracellular FITC-dextran is present in soluble form, while PI is predominantly bound to nucleic acids. A broad, statistically significant distribution of molecular uptake was also observed. Such quantitative determinations should be important for guiding applications of electroporation, and for testing models of electroporation mechanisms. Further, the use of PI, which is well established as a membrane exclusion dye, provides additional support for the interpretation that both PI and FITC-dextran were internalized as a result of an electrical pulse.

Binding Sites↗
PubMed1989

Tissue electroporation. Observation of reversible electrical breakdown in viable frog skin.

Experiments by others have used isolated cell or bilayer membrane preparations to study the dramatic phenomena associated with electroporation. The present study observes electroporation behavior in an intact tissue. Viable samples of frog skin (Rana pipiens) were exposed to short electrical pulses of varying width and magnitude under "charge injection" conditions. After a pulse, the transtissue potential decayed with two distinct time constants, one short (tau approximately 0.3 ms) and the other longer (tau L approximately 2 ms). Above thresholds for the pulse magnitude and for the pulse width tau L decreased significantly, with progressively smaller tau L as the pulse magnitude and width increased. The postpulse potential, delta Utissue (t), and resistance, Rtissue, also decreased progressively. The tissue subsequently recovered to its original resistance and open circuit potential, delta U tissue,oc, within 2-3 min after a pulse. At that time another pulse experiment could be carried out, demonstrating repeatability and reversibility. No significant permanent changes in Rtissue and delta Utissue,oc were found. This is interpreted as avoidance of significant tissue damage. Taken together, these dramatic phenomena are characteristic of the reversible electrical breakdown previously observed in charge injection experiments with artificial planar bilayer membranes and with isolated cell membranes by similar very short pulses. The present experiments therefore demonstrate that electroporation can be repeatedly caused and observed in a viable tissue without apparent damage.

Animals↗
PubMed1988

Electroporation: high frequency of occurrence of a transient high-permeability state in erythrocytes and intact yeast.

We present the first determinations of population distributions of macromolecule uptake due to electroporation, the percentage of cells which participate and, for the yeast, the subpopulation of cells whose membranes exhibit significant recovery following macromolecule uptake. Flow cytometry is used to measure the uptake of a first test molecule (green fluorescence, FITC-dextran; 70 kDa) and also, for the yeast, the subsequent uptake of a second, much smaller, test molecule (red fluorescence, propidium iodide; 660 Da), which provides a measure of membrane recovery. A dramatic 20% (erythrocytes) to 75% (intact Schizosaccharomyces pombe) of cells can take up the first test molecule within 5 min of a pulse.

Cell Membrane Permeability↗
PubMed1985

Enzyme electrodes and related technologies.

The technical outlook is promising for miniature analytical systems which are internally complex but externally simple. Salient features to be anticipated are: The use of miniature electrodes or other sensors in combination with enzymes or immunological compounds for biochemical specificity. The use of arrays of miniature electrodes or other sensors. Relatively low cost because of adaptation of semiconductor fabrication techniques. The attendant possibility of the devices being disposable. The intimate involvement of real time computation. The use of simultaneous replicate assays, with increased confidence in the accuracy of the assay. Overall, rapid assays. Because of these possibilities, it may be concluded that the technological outlook for conducting clinical chemistry assays nearer the patient is promising.

Chromatography, Gas↗
PubMed1977

Protein, casein, and noncasein protein percentages in milk with high somatic cell counts.

More than 1000 milk samples of individual cows with somatic cell counts ranging from 20,000 to 20,000,000 per ml were analyzed by amido black dye binding for total protein, whey protein, and casein. Ten classes of varying somatic cell counts were established. The mean total protein percentage for normal samples (counts less than 500,000/ml) was 3.2% and different from all the other protein class means, ranging from 3.4 to 3.9%. Total protein content increased with somatic cell count. There was no significant difference among any of the ten classes for casein values. Whey protein percentages for normal samples were different from the rest. Whey protein content increased with somatic cell count.

Animals↗
PubMed1977

Pericardial drainage operations in the management of uremic pericardial effusion.

Because of frequent failures in nonoperative therapy, we have adopted early surgical drainage of the pericardium in the management of uremic pericardial effusion. This series presents the longest follow-up period of any group of patients with uremic pericardial effusion treated by surgical drainage. There have been no intraoperative deaths and no recurrences. The total hospital mortality rate was 8.3 per cent and the late mortality rate over a 72 month period was 25 per cent. Internal pericardiostomy drainage is a simple yet effective surgical solution to the life-threatening problem of uremic pericardial effusion.

Drainage↗
PubMed1976

Experiments and calculations concerning a thermal enzyme probe.

A simple device capable of measuring almost any reactant in an enzyme-catalyzed reaction is created when an enzyme is immobilized onto one thermal sensor of a differential thermometer. Experiments are described in which two thermistors, one bare and one coated with immobilized enzyme, are immersed in a well-stirred solution. The response of this device to increases in glucose-ATP concentration was observed using hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1), and to increases in glucose concentration using glucose oxidase (beta-D-glucose:oxygen 1-oxidoreductase, EC 1.1.3.4). A simple model is presented whose predictions are in reasonable agreement with the experimental results.

Enzymes, Immobilized↗