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Biomedical subjects

C C Davis

Publications and source records attributed to C C Davis.

At least 37 records · Page 2Linked to original sources
PubMed1998

BIGEL analysis of gene expression in HL60 cells exposed to X rays or 60 Hz magnetic fields.

We screened a panel of 1,920 randomly selected cDNAs to discover genes that are differentially expressed in HL60 cells exposed to 60 Hz magnetic fields (2 mT) or X rays (5 Gy) compared to unexposed cells. Identification of these clones was accomplished using our two-gel cDNA library screening method (BIGEL). Eighteen cDNAs differentially expressed in X-irradiated compared to control HL60 cells were recovered from a panel of 1,920 clones. Differential expression in experimental compared to control cells was confirmed independently by Northern blotting of paired total RNA samples hybridized to each of the 18 clone-specific cDNA probes. DNA sequencing revealed that 15 of the 18 cDNA clones produced matches with the database for genes related to cell growth, protein synthesis, energy metabolism, oxidative stress or apoptosis (including MYC, neuroleukin, copper zinc-dependent superoxide dismutase, TC4 RAS-like protein, peptide elongation factor 1alpha, BNIP3, GATA3, NF45, cytochrome c oxidase II and triosephosphate isomerase mRNAs). In contrast, BIGEL analysis of the same 1,920 cDNAs revealed no differences greater than 1.5-fold in expression levels in magnetic-field compared to sham-exposed cells. Magnetic-field-exposed and control samples were analyzed further for the presence of mRNA encoding X-ray-responsive genes by hybridization of the 18 specific cDNA probes to RNA from exposed and control HL60 cells. Our results suggest that differential gene expression is induced in approximately 1% of a random pool of cDNAs by ionizing radiation but not by 60 Hz magnetic fields under the present experimental conditions.

DNA Damage↗
PubMed1997

Intracellular calcium signaling by Jurkat T-lymphocytes exposed to a 60 Hz magnetic field.

To explore possible biochemical mechanisms whereby electromagnetic fields of around 0.1 mT might affect immune cells or developing cancer cells, we studied intracellular calcium signaling in the model system Jurkat E6-1 human T-leukemia cells during and following exposure to a 60 Hz magnetic field. Cells were labeled with the intracellular calcium-sensitive fluorescent dye Fluo-3, stimulated with a monoclonal antibody against the cell surface structure CD3 (associated with ligand-stimulated T-cell activation), and analyzed on a FACScan flow-cytometer for increases in intensity of emissions in the range of 515-545 nm. Cells were exposed during or before calcium signal-stimulation to 0.15 mTrms 60 Hz magnetic field. The total DC magnetic field of 78.2 microT was aligned 17.5 degrees off the vertical axis. Experiments used both cells cultured at optimal conditions at 37 degrees C and cells grown under suboptimal conditions of 24 degrees C, lowered external calcium, or lowered anti-CD3 concentration. These experiments demonstrate that intracellular signaling in Jurkat E6-1 was not affected by a 60 Hz magnetic field when culture and calcium signal-stimulation were optimal or suboptimal. These results do not exclude field-induced calcium-related effects further down the calcium signaling pathway, such as on calmodulin or other calcium-sensitive enzymes.

Calcium↗
PubMed1996

Rodent cell transformation and immediate early gene expression following 60-Hz magnetic field exposure.

Some epidemiological studies suggest that exposure to power frequency magnetic fields (MFs) may be associated with an elevated risk of human cancer, but the experimental database remains limited and controversial. We investigated the hypothesis that 60-Hz MF action at the cellular level produces changes in gene expression that can result in neoplastic transformation. Twenty-four hour 200 microT continuous MF exposure produced negative results in two standard transformation systems (Syrian hamster embryo cells and C3H/10T1/2 murine fibroblasts) with or without postexposure to a chemical promoter. This prompted a reexamination of previously reported MF-induced changes in gene expression in human HL60 cells. Extensive testing using both coded and uncoded analyses was negative for an MF effect. Using the same exposure conditions as in the transformation studies, no MF-induced changes in ornithine decarboxylase expression were observed in C3H/10T1/2 cells, casting doubt on a promotional role of MF for the tested cells and experimental conditions.

Animals↗
PubMed1994

Microwave dielectric measurements of erythrocyte suspensions.

Complex dielectric constants of human erythrocyte suspensions over a frequency range from 45 MHz to 26.5 GHz and a temperature range from 5 to 40 degrees C have been determined with the open-ended coaxial probe technique using an automated vector network analyzer (HP 8510). The spectra show two separate major dispersions (beta and gamma) and a much smaller dispersion between them. The two major dispersions are analyzed with a dispersion equation containing two Cole-Cole functions by means of a complex nonlinear least squares technique. The parameters of the equation at different temperatures have been determined. The low frequency behavior of the spectra suggests that the dielectric constant of the cell membrane increases when the temperature is above 35 degrees C. The real part of the dielectric constant at approximately 3.4 GHz remains almost constant when the temperature changes. The dispersion shifts with temperature in the manner of a thermally activated process, and the thermal activation enthalpies for the beta- and gamma-dispersions are 9.87 +/- 0.42 kcal/mol and 4.80 +/- 0.06 kcal/mol, respectively.

Calorimetry↗
PubMed1994

Femoropopliteal bypass with externally supported knitted Dacron grafts: a follow-up of 200 grafts for one to twelve years.

PURPOSE: This article reports our experience with externally supported, preclotted knitted Dacron grafts in femoropopliteal bypass. METHODS: This is a retrospective analysis of a consecutive series of 154 patients who received 200 grafts (175 above knee and 25 below knee). Follow-up extended to 12 years (mean 59 1/2 months). RESULTS: Primary patency rates for the entire series were 75%, 70%, and 47% at 3, 5, and 10 years, respectively. Above-knee grafts had 76%, 71%, and 50% rates and 3, 5, and 10 years, respectively. Below-knee grafts had 65% and 57% at 3 and 5 years, respectively. Limb-salvage rates were 87%, 79%, and 73% at 3, 5, and 10 years, respectively, for the 57 limbs operated on because of critical ischemia. The most significant predictor of graft failure was poor runoff as determined by preoperative arteriography. The effect of poor runoff was most pronounced in the first 3 months. CONCLUSION: Externally supported, preclotted knitted Dacron grafts provide encouraging primary patency rates for above-knee femoropopliteal bypass. Poor leg vessel runoff is a major determinant of early graft failure.

Adult↗
PubMed1994

Two-point electrical-fluorescence recording from heart with optical fibers.

Optical recordings from frog myocardium, stained with a voltage-sensitive dye, have been made through a fiber optic system that uses fiber couplers to provide two excitation/detection paths and to separate excitation light from the fluorescence signal. The excitation light, from a green He-Ne laser (543 nm), is focused into a 100 microns-core fiber then is split 1:1 to two other fibers. Each of these two fibers transmits part of the excitation light through a fiber coupler (1:15 transmittance ratio) to the heart preparation which is stained with the voltage-sensitive dye RH237. The returning red fluorescence is split at the same fiber coupler (15:1 transmittance ratio) and is directed to a photomultiplier tube through a longpass filter. With this two-point mapping method, differences in action potential shape and timing have been observed.

Action Potentials↗
PubMed1993

Axillofemoral bypass with externally supported, knitted Dacron grafts: a follow-up through twelve years.

PURPOSE: The purpose of this study was to review our experience with externally supported, knitted Dacron grafts used for axillofemoral bypass. METHODS: Retrospective analysis was performed on records of 79 consecutive axillofemoral bypass graft operations performed on 77 patients from January 1978 to April 1990. RESULTS: The mortality rate within 30 days of operation was 5% (four of 79); 36 patients died in the follow-up period; none died of graft causes. During this 12-year period (mean follow-up 42 months) three patients were unavailable for follow-up. The primary patency rate was 78% at 5 years and 73% at 7 years, with no change thereafter. Neither the graft configuration (i.e., axillounifemoral [n = 50] vs axillobifemoral [n = 29]) nor patency of the superficial femoral artery had an impact on the primary patency rate. Patients who underwent surgery for disabling claudication (n = 30 grafts) had a primary patency rate of 80% at 6 years compared with 65% at 6 years for those who required surgery for limb salvage (n = 49 grafts); the difference was not significant (p = 0.37). Actuarial survival of patients with axillofemoral grafts was 23% at 10 years compared with 72% in a concurrent population of patients with aortofemoral bypass (p < 0.001). CONCLUSION: These findings indicate that axillofemoral bypass grafts may be appropriate for high-risk patients with severe aortoiliac disease who require revascularization for either limb salvage or incapacitating claudication.

Adult↗
PubMed1993

Impedance spectroscopy of human erythrocytes: system calibration and nonlinear modeling.

We present in detail our impedance measurement method, the cell embodding technique, for human erythrocytes, and an accurate calibration procedure for a true four-electrode impedance measurement system. This technique with the calibration procedure gives reliable impedance measurements over a wide frequency range--1 Hz to 10 MHz. To achieve high sensitivity in this frequency range, we embed the cells in the pores of a Nuclepore filter. The calibration procedure assumes that the measurement system is linear, and requires measurement of three reference impedances. The reliability of this procedure is demonstrated with various RC circuits, and application of it to the bio-impedancae measurement system eliminates a quasi-dispersion in the high-frequency range, and increases the bandwidth at both the low- and high-frequency ends of the range by about a decade. We model the impedance of the cells embedded within the filter with an equivalent circuit that is consistent with the geometry and interfaces present. The experimental data are fitted to this model by means of a complex nonlinear least squares (CNLS) fit, which simultaneously fits the real and imaginary parts of the impedance with the Levenberg-Marquardt algorithm. The impedance spectra of human erythrocytes are found to display constant-phase-angle (CPA) characteristics. A CPA element is an impedance of the form Z = A/(jw) alpha, where A is a constant, j = square root -1, omega is angular frequency, and 0 < alpha < 1, and has been used to describe the ac response of the interface between the cell surface and the external electrolyte solution. Such a CPA element may be related to fractal character of the interface.

Calibration↗
PubMed1992

Effects of continuous and pulsed 2450-MHz radiation on spontaneous lymphoblastoid transformation of human lymphocytes in vitro.

Normal human lymphocytes were isolated from the peripheral blood of healthy donors. One-ml samples containing (10(6)) cells in chromosome medium 1A were exposed for 5 days to conventional heating or to continuous wave (CW) or pulsed wave (PW) 2450-MHz radiation at non-heating (37 degrees C) and various heating levels (temperature increases of 0.5, 1.0, 1.5, and 2 degrees C). The pulsed exposures involved 1-microsecond pulses at pulse repetition frequencies from 100 to 1,000 pulses per second at the same average SAR levels as the CW exposures. Actual average SARs ranged to 12.3 W/kg. Following termination of the incubation period, spontaneous lymphoblastoid transformation was determined with an image analysis system. The results were compared among each of the experimental conditions and with sham-exposed cultures. At non-heating levels, CW exposure did not affect transformation. At heating levels both conventional and CW heating enhanced transformation to the same extent and correlate with the increases in incubation temperature. PW exposure enhanced transformation at non-heating levels. This finding is significant (P less than .002). At heating levels PW exposure enhanced transformation to a greater extent than did conventional or CW heating. This finding is significant at the .02 level. We conclude that PW 2450-MHz radiation acts differently on the process of lymphoblastoid transformation in vitro compared with CW 2450-MHz radiation at the same average SARs.

Hot Temperature↗
PubMed1992

Frequency domain impedance measurements of erythrocytes. Constant phase angle impedance characteristics and a phase transition.

We report measurements of the electrical impedance of human erythrocytes in the frequency range from 1 Hz to 10 MHz, and for temperatures from 4 to 40 degrees C. In order to achieve high sensitivity in this frequency range, we embedded the cells in the pores of a filter, which constrains the current to pass through the cells in the pores. Based on the geometry of the cells embedded in the filter a circuit model is proposed for the cell-filter saline system. A constant phase angle (CPA) element, i.e., an impedance of the form Z = A/(j omega)alpha, where A is a constant, j = square root of -1, omega is angular frequency, and 0 less than alpha less than 1 has been used to describe the ac response of the interface between the cell surface and the electrolyte solution, i.e., the electrical double layer. The CPA and other elements of the circuit model are determined by a complex nonlinear least squares (CNLS) fit, which simultaneously fits the real and imaginary parts of the experimental data to the circuit model. The specific membrane capacitance is determined to be 0.901 +/- 0.036 microF/cm2, and the specific cytoplasm conductivity to be 0.413 +/- 0.031 S/m at 26 degrees C. The temperature dependence of the cytoplasm conductivity, membrane capacitance, and CPA element has been obtained. The membrane capacitance increases markedly at approximately 37 degrees C, which suggests a phase transition in the cell membrane.

Biophysical Phenomena↗
PubMed1992

Flanged coaxial microwave probes for measuring thin moisture layers.

We obtain an analytical, closed-form expression for the input admittance of a flanged, open-ended coaxial line radiating into a layered lossy material. The effect of higher modes as well as the dominant mode have been taken into consideration. The results obtained in the experimental measurement of the microwave reflection coefficient of the probe radiating into very thin water layers are described and compared with the results obtained from numerical calculations based on a theoretical model. The measurements were made in the 5.0-7.0 GHz range. The results demonstrate, for example, the usefulness of this type of device in measuring thin moisture layers in the outer layer of the human skin.

Body Water↗
PubMed1991

Excitation and detection of action potential-induced fluorescence changes through a single monomode optical fiber.

An optical probe capable of detecting intracellular potential changes in individual cells, in vitro, which has the potential for in vivo applications, has been developed. A single-mode optical fiber directs laser light onto cells stained with the voltage-sensitive fluorescent dye, WW781 and also returns part of the resulting fluorescence to a detection system. Frog cardiac cells in vitro were used in these initial experiments. The fractional change in fluorescent intensity of 10(-3) for a 50 mV shift in transmembrane potential obtained from a heart immobilized in zero calcium Ringer's solution is comparable to that reported for other optical methods. For hearts in normal calcium Ringer's solutions, very large reproducible motion related artifacts were detected.

Animals↗
PubMed1991

A model of pneumococcal pneumonia in chronically intoxicated rats.

To determine the role of chronic ethanol intoxication on the pathogenesis of pneumococcal pneumonia, male Sprague-Dawley rats were fed an ethanol-containing diet for 1 week before intratracheal challenge with type 3 Streptococcus pneumoniae and for 10 days after infection. Control rats were fed the same diet except that ethanol was replaced isocalorically with carbohydrate. Ethanol treatment increased pneumococcal bacteremia, levels of capsular polysaccharide antigenemia, and susceptibility to lethal pneumonia. Once dissemination occurred, ethanol-fed rats failed to eliminate pneumococci from the bloodstream. Ethanol-fed rats demonstrated a defect in late pulmonary clearance of pneumococci that was temporally associated with a significantly higher pneumonia severity index. Pneumonia was characterized by an intense polymorphonuclear leukocyte infiltration, severe edema, and a fibrous exudate. Bronchoalveolar lavage confirmed the heightened inflammatory response in the lungs of ethanol-fed rats, suggesting that chronic ethanol intoxication did not impair polymorphonuclear leukocyte recruitment but may alter their antipneumococcal functions.

Alcoholism↗
PubMed1989

An automated dosimetry system for microwave and thermal exposure of biological samples in vitro.

A waveguide exposure system with automated sample temperature measurement is described. This system provides on-line determination of the temperature profile over time of biological samples in vitro. It allows automated computation of the specific absorption rate determined from heating/cooling curves, uses minimally-perturbing thermometry, is biocompatible and can be used for measurements of both microwave and conventional heating.

Electronic Data Processing↗
PubMed1989

Toddlers' emerging ways of achieving social coordinations with a peer.

14 peer dyads were observed longitudinally at 16, 20, 24, 28, and 32 months to assess developmental changes in social coordinations (both action-to-action thematic relations and extended games). Each child's movements through the playroom, actions upon play material, vocalizations, verbalizations, and gestures were coded for their relation to the concurrent or immediately prior behavior of the peer: Unrelated, Tangential, Coordinated, Interfering. There was a marked increase with age in acts coordinated with those of a peer, and imitations of the peer's nonverbal actions accounted for most of the developmental change. The use of words to direct the peer in a coordinated way increased with age but remained infrequent. Developmental change in the frequency of games paralleled that for imitative acts, and imitative acts both established and set the theme for most of the games. Thus, imitating another's nonverbal actions is a core behavioral strategy for achieving social coordinations during the developmental period preceding reliance on verbal communication in peer interaction.

Child Development↗
PubMed1987

Microwave effects on plasmid DNA.

The exposure of purified plasmid DNA to microwave radiation at nonthermal levels in the frequency range from 2.00 to 8.75 GHz produces single- and double-strand breaks that are detected by agarose gel electrophoresis. Microwave-induced damage to DNA depends on the presence of small amounts of copper. This effect is dependent upon both the microwave power and the duration of the exposure. Cuprous, but not cupric, ions were able to mimic the effects produced by microwaves on DNA.

Copper↗
PubMed1986

Healing basis and surgical techniques for complete revascularization of the left ventricle using only the internal mammary arteries.

Long-term follow-up data from several leading centers concerning patients undergoing coronary artery bypass clearly demonstrate the superiority of the internal mammary artery (IMA) with patency rates of 83 to 94% at 7 to 12 years compared with the saphenous vein and its patency rates of 41 to 53%. Our experimental studies provide a biological basis for understanding this difference. Thin-walled arterial autografts undergo no histological change after being implanted in the arterial system, while venous autografts undergo major changes with an initial scattered loss of endothelium and marked thickening due to a proliferative reaction. The challenge to the cardiac surgeon is to revascularize the entire left ventricle with the IMAs. We have found this possible in most patients with advanced three-vessel disease by using both IMAs either as in situ grafts or free grafts with as many sequential anastomoses as necessary to achieve full revascularization. Our use of the term in situ refers to the graft's origin from the subclavian artery as opposed to a free IMA graft arising from another site.

Aged↗