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J H Davis

Publications and source records attributed to J H Davis.

At least 91 records · Page 5Linked to original sources
PubMed1990

Phase equilibria of cholesterol/dipalmitoylphosphatidylcholine mixtures: 2H nuclear magnetic resonance and differential scanning calorimetry.

Deuterium nuclear magnetic resonance spectroscopy and differential scanning calorimetry are used to map the phase boundaries of mixtures of cholesterol and chain-perdeuteriated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine at concentrations from 0 to 25 mol % cholesterol. Three distinct phases can be identified: the L alpha or liquid-crystalline phase, the gel phase, and a high cholesterol concentration phase, which we call the beta phase. The liquid-crystalline phase is characterized by highly flexible phospholipid chains with rapid axially symmetric reorientation; the gel phase has much more rigid lipid chains, and the motions are no longer axially symmetric on the 2H NMR time scale; the beta phase is characterized by highly ordered (rigid) chains and rapid axially symmetric reorientation. In addition, we identify three regions of two-phase coexistence. The first of these is a narrow L alpha/gel-phase coexistence region lying between 0 and about 6 mol % cholesterol at temperatures just below the chain-melting transition of the pure phospholipid/water dispersions, at 37.75 degrees C. The dramatic changes in the 2H NMR line shape which occur on passing through the phase transition are used to map out the boundaries of this narrow two-phase region. The boundaries of the second two-phase region are determined by 2H NMR difference spectroscopy, one boundary lying near 7.5 mol % cholesterol and running from 37 down to at least 30 degrees C; the other boundary lies near 22 mol % cholesterol and covers the same temperature range. Within this region, the gel and beta phases coexist. As the temperature is lowered below about 30 degrees C, the phospholipid motions reach the intermediate time scale regime of 2H NMR so that spectral subtractions become difficult and unreliable. The third two-phase region lies above 37 degrees C, beginning at a eutectic point somewhere between 7.5 and 10 mol % cholesterol and ending at about 20 mol %. In this region, the L alpha and beta phases are in equilibrium. The boundaries for this region are inferred from differential scanning calorimetry traces, for the boundary between the L alpha- and the two-phase region, and from a dramatic sharpening of the NMR peaks on crossing the boundary between the two-phase region and the beta-phase region. In this region, the technique of difference spectroscopy fails, presumably because the diffusion rate in both the L alpha- and beta-phase domains is so rapid that phospholipid molecules exchange rapidly between domains on the experimental time scale.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1989

Orientation of alpha-helical peptides in a lipid bilayer.

Samples of pure lipid (dipalmitoylphosphatidylcholine) and lipid containing short alpha-helical peptides were oriented and examined by X-ray diffraction, together with unoriented samples of pure peptide. X-ray reflections from the bilayer and the alpha-helices showed that the peptides had oriented in the bilayer with their helical axes perpendicular to the surface.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1989

Flow cytometric analysis of mature adipocytes.

Flow cytometry is an excellent method for studying the physiological function in adipocytes because their response to hormones, especially insulin, varies with cell maturity and therefore size. Adipocytes present a unique technical challenge. A freshly prepared adipocyte suspension contains cells and fat droplets ranging from 10 to greater than 120 microns in diameter. Stored fat occupies 90-98% of the cell volume, making it difficult to distinguish cells from fat droplets. Other difficulties include buoyancy, large size, fragility, and tendency to aggregate and clog the sample tube and nozzle. These obstacles were overcome by 1) maintaining the sample, sample line, sheath fluid, reservoir, and nozzle assembly at 37 degrees C; 2) using a 200 microns diameter orifice; 3) using a short, 300 microns inside diameter Teflon sample delivery line; 4) injecting the sample at constant flow rate into the sheath fluid at low pressure; and 5) using the pH-sensitive vital stain, biscarboxyethylcarboxyfluorescein (BCECF) to distinguish cells from fat droplets. Stained cells are brightly fluorescent when excited at 488 nm. Because fat droplets do not fluoresce, they can be distinguished from fat cells by gating on the BCECF emission. The cytosolic pH of intact, viable, mature adipocytes was derived from the ratio of the fluorescent emission intensities at 520 and 620 nm and was estimated to be 7.2. Unlike BCECF, several other useful fluorescent probes of cell function, e.g., the intracellular calcium indicator, indo-1, label both fat cells and fat droplets.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1989

Two six-shot suicides in close geographic and temporal proximity.

Two six-shot suicides are reported that occurred in adjoining counties in Ohio eleven-and-one-half weeks apart. There is no indication of any connection between victims, and it is doubtful that the second individual knew of the first death since there was no news media coverage of the first death. The most significant points of commonality between the two cases are the location of the gunshot wounds (anterior chest and upper abdomen) and the responses of disbelief from those outside the medicolegal professions. Knowledge of such cases with a high number of shots and more than one fatal wound can assist death investigators in confronting similar cases.

Abdominal Injuries↗
PubMed1988

Differential scanning calorimetry and 2H NMR studies of the phase behavior of gramicidin-phosphatidylcholine mixtures.

The extents of two-phase coexistence in the phase diagrams of mixtures of gramicidin with 1,2-bis(perdeuteriopalmitoyl)-sn-glycero-3-phosphocholine (DPPC-d62) and with 1,2-bis(perdeuteriomyristoyl)-sn-glycero-3-phosphocholine (DMPC-d54) mixtures have been explored with differential scanning calorimetry (DSC) and deuterium nuclear magnetic resonance (2H NMR). For both systems, increased gramicidin content causes a decrease in transition enthalpy and a broadening of the peak in excess heat capacity at the transition. In DMPC-d54-based mixtures, the broadening is roughly symmetric about the pure lipid transition temperature. Addition of gramicidin to DPPC-d62 extends the excess heat capacity peak on the low-temperature side, resulting in a slightly asymmetric scan. Deuterium NMR spectra showing a superposition of gel and liquid-crystalline components, observed for both mixtures, indicate the presence of two-phase coexistence. For the DPPC-d62-based mixtures, two-phase coexistence is restricted to an approximately 2 degrees C temperature range below the pure transition temperature. For DMPC-d54-based mixtures, the region of two-phase coexistence is even narrower. For both mixtures, beyond a gramicidin mole fraction of 2%, distinct gel and liquid-crystal contributions to the spectra cannot be distinguished. Along with the broad featureless nature of the DSC scan in this region, this is taken to indicate that the transition has been replaced by a continuous phase change. These results are consistent with the existence of a closed two-phase region having a critical concentration of gramicidin below 2 mol%.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1988

2H nuclear magnetic resonance of exchange-labeled gramicidin in an oriented lyotropic nematic phase.

Lyotropic nematic liquid-crystalline phases, such as that formed by potassium laurate/decanol/KCl/water, are found to accept readily large amphiphilic solute molecules. Since these phases spontaneously orient in high magnetic fields, it becomes possible to obtain NMR spectra of biologically interesting solutes in an oriented axially symmetric environment. The amide hydrogens of the peptide backbone of gramicidin D (Dubos) were exchanged for deuterium, and the gramicidin was incorporated into a lyotropic nematic phase made with deuteriated buffer in place of water. 2H NMR spectra of oriented, exchange-labeled gramicidin were then obtained. The strong water signal from the deuteriated buffer was eliminated by using selective excitation and a polynomial subtraction procedure. The 2H NMR spectra at high temperature consist of twelve major quadrupolar doublets. The splittings observed are largely independent of temperature, suggesting a highly rigid backbone structure. Two of the doublets, which are chemically shifted relative to the others, show stronger temperature dependence. These two probably arise from the exchangeable amino hydrogens on the tryptophan indole moieties of the peptide. While we cannot yet assign all of the doublets, the spectra and nuclear magnetic relaxation data are consistent with a rigid slightly distorted beta LD6.3 helix undergoing axially symmetric reorientation about the director of the liquid-crystalline phase. The correlation time for the axially symmetric reorientation is determined by relaxation measurements to be about 10(-7) s.

Deuterium↗
PubMed1988

A study of mothers' postpartum teaching priorities.

This descriptive study investigated the teaching priorities of mothers during the early puerperium. Subjects (N = 117) were English-speaking women who had normal vaginal deliveries and healthy newborns. A questionnaire consisting of 16 maternal and 23 infant care teaching topics was administered during the 3-day postpartum hospital stay. Respondents rated each topic's teaching priority on a 4-point, Very Important to Not Very Important, scale. Results were analyzed with percentages in relation to all mothers, maternal age groups (teens, twenties, thirties), and parity groups (primiparas, multiparas). The maternal care topic of highest priority for all age and parity groups was "Postpartum Complications." The infant care topic of highest priority for all age and parity groups was "Infant Illnesses." The results suggest that these teaching topics are of most concern to mothers during the early postpartum period. The mothers' priorities assigned to other teaching topics varied by age and parity groups.

Adolescent↗
PubMed1987

Relationship between Russian roulette deaths and risk-taking behavior: a controlled study.

A review of medical examiner records yielded data on 19 men and one woman who died playing Russian roulette. The men differed significantly from 95 male suicide victims who died of gunshot wounds to the head on several variables including age, race, ethnicity, religion, citizenship, marital status, living situation, health, and the likelihood of the death being witnessed. The Russian roulette victims were significantly less likely to die in the bedroom, die in the morning, leave a suicide note, and be depressed but were significantly more likely to have alcohol or drugs in their body fluids and to have a previous history of drug and alcohol abuse.

Adult↗
PubMed1987

Complications of cardiac resuscitation.

In a prospective study of the complications of cardiac resuscitation, 705 cases were autopsied to identify the cause of death and the pathologic findings attributable to cardiac resuscitation. Thoracic complications were observed in 42.7 percent of the cases. A total of 31.6 percent had rib fractures, 21.1 percent had sternal fractures, and 18.3 percent were reported as having anterior mediastinal hemorrhage; 20.4 percent of the cases had an upper airway complication. Abdominal visceral complications were noted in 30.8 percent of the cases, and pulmonary complications occurred in 13 percent of the resuscitation population. Life-threatening complications, such as heart and great vessel injuries, occurred in less than .5 percent of the cases.

Abdominal Injuries↗
PubMed1986

Studies on the interaction of human erythrocyte band 3 with membrane lipids using deuterium nuclear magnetic resonance and differential scanning calorimetry.

Human erythrocyte band 3, reconstituted into large unilamellar phospholipid vesicles, has been used as a model system for studying the interactions between membrane lipids and large transmembrane glycoproteins. Both 2H-nuclear magnetic resonance (2H-NMR) and differential scanning calorimetric techniques have been used to probe dimyristoylphosphatidylcholine-band 3 interactions over the temperature range 4-32 degrees C. Analysis of 2H-NMR spectra allowed the assignment of liquid crystal, gel phase and two-phase regions for several protein/lipid mole fractions in the range (1-20) X 10(-4). Sample size was limited by the amount of available glycoprotein and this precluded exact determination of the phase boundaries for this system. The sharp discontinuity in the spectral first moment, M1, seen at the phase transition of the pure phospholipid is progressively diminished by addition of protein, and at the highest protein concentration the first moment varies smoothly between the two phases. For T greater than 26 degrees C or less than 16 degrees C, the moments are relatively insensitive to protein concentration, while between 20 and 26 degrees C the moments increase with protein concentration up to the boundary of the two-phase region. Beyond this boundary, they remain constant or decrease slightly with increasing amount of protein. A preliminary phase diagram for band 3 in this lipid system is presented, based on 2H-NMR data. Differential scanning calorimetry (DSC) showed that addition of glycoprotein dramatically alters the scan shape and tends to extend the coexistence of two phases to higher temperatures.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1986

Decreasing the incidence of surgical wound infections. Validation of a surveillance-notification program.

In an attempt to validate the observations of a previously published ten-year study of surgical wounds, we studied 8,474 wounds over an 18-month period using a protocol nearly identical to that of the previous study. Our study corroborated the following predictors of clean-wound infection: increasing duration of surgery, age less than 1 or greater than 50 years, increasing duration of preoperative hospitalization, use of drains, and shaving and emergency surgery. We failed to corroborate use of wound irrigation as a protective measure or time of preoperative shaving as a significant variable. Most importantly, we found a 42% reduction in the clean-wound infection rate during the study period (1.9% to 1.1%), adding support to the concept that a wound surveillance program with surgeon notification is both efficacious and cost-effective.

Adolescent↗
PubMed1986

Bodies found in the water. An investigative approach.

The determination of the cause of death of a person whose body is found in the water requires careful investigative work on the part of both police and pathologists. Opinions as to cause and manner of death should not be derived from the autopsy alone but must result from a logical correlation of data regarding victim identity, circumstances, autopsy, and laboratory findings.

Child↗