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Biomedical subjects

L E Moore

Publications and source records attributed to L E Moore.

At least 91 records · Page 5Linked to original sources
PubMed1975

Potassium-ion conduction noise in squid axon membrane.

Spectral analysis (1-1000 Hz) of spontaneous fluctuations of potential and current in small areas of squid (Loligo pealei) axon shows two forms of noise: f-1 noise occurs in both excitable and inexcitable axons with an intensity which depends upon the driving force for potassium ions. The other noise has a spectral form corresponding to a relaxation process, i.e. its asymptotic behavior at low frequencies is constant, and at high frequencies it declines with a slope of -2. This latter noise occurs only in excitable axons and was identified in spectra by (1) its disappearance after reduction of K+ current by internal perfusion with solutions containing tetraethylammonium (TEA+), Cs+ or reduced [Ki+] and (2) its insensitivity to block of Na+ conduction and active transport. The transition frequency of relaxation spectra are also voltage and temperature dependent and relate to the kinetics of K+-conduction in the Hodgkin-Huxley formulation. These data strongly suggest that the relaxation noise component arises from the kinetic properties of K+ channels. The f-1 noise is attributed to restricted diffusion in conducting K+ channels and/or leakage pathways. In addition, an induced K+ conduction noise associated with the binding of TEA+ and triethyldecylammonium ion to membrane sites is described. Measurement of the induced noise may provide an alternative means of characterizing the kinetics of interaction of these molecules with the membrane and also suggests that these and other pharmacological agents may not be useful in identifying noise components related to the sodium conduction mechanism which, in these experiments, appears to be much lower in intensity than either the normal K conduction or induced noise components.

Animals↗
PubMed1975

Light scattering spectroscopy of the squid axon membrane.

Light scattering studies on the giant squid axon were done using the technique of optical mixing spectroscopy. This experimental approach is based on the use of laser light to detect the fluctuations of membrane macromolecules which are associated with conductance fluctuations. The light scattering spectra were similar to the Lorentzian-like behavior of conductance fluctuations, possibly reflecting an underlying conformational change in the specific membrane sites responsible for the potassium ion conductance. The amplitude of the spectra measured, increased when the membrane was depolarized and decreased on hyperpolarization. The spectra were fit to the sum of two terms, a (1/f component and a simple Lorentzian term. Spectra from deteriorating axons did not show sensitivity to membrane potential changes. It is shown theoretically that fluctuations due to the voltage-dependent variable, n, of the Hodgkin-Huxley formalism are identical to the voltage fluctuations. The derived power spectrum is that of a second order system, capable of showing resonance peaking only if the voltage dependence of the potassium rate of constants is included in the analysis. The lack of resonance peaking in the observed light scattering spectra, indicates that the data are best described by a damped second order system.

Animals↗
PubMed1975

Membrane conductance changes in single nodes of Ranvier, measured by laser-induced temperature-jump experiments.

Temperature-jump experiments on isolated myelinated nerve fibers were done using a pulsed laser system in the Q switched mode. Voltage-clamp and temperature perturbations were used to measure the relaxing ionic conductances of both the Na+ and K+ systems. It is shown that the T jump can be used to probe the K+ and Na+ conductances during non-steady state conditions and thereby elicit relaxation times for a variety of initial states. Temperature-induced K+ conductance relaxation times were consistent with voltage-clamp measurements. The temperature-perturbation experiments were done as a combination of a temperature step and impulse change due to an adsorption of carbon black particles on the nerve. The experiments support the hypothesis that the relaxation times of the K+ system are independent of the previous history of the axon. It is concluded that the K+ conductance is at least a second-order system whose relaxation spectrum is composed of two exponential terms the magnitudes of which are markedly dependent on the initial conditions.

Animals↗
PubMed1972

Laser temperature-jump technique for relaxation studies of the ionic conductances in myelinated nerve fibers.

A temperature-jump technique for single nodes of Ranvier has been developed using a pulsed laser system. The temperature perturbation was accomplished by firing the laser beam obtained from a neodymium rod through the solution surrounding a single node. The temperature step was achieved within 1 msec using the laser in the normal mode of operation. During the voltage-clamped steady-state current a temperature jump from 4 degrees C increased the current to a new steady-state value within the time course of the T-jump. This finding suggests that the maximum potassium permeability P(K) has a rapid relaxation time and that the steady-state value of n (the value of potassium permeability divided by its maximum value) is relatively independent of temperature. T-jumps applied during the voltage-clamped sodium currents showed that the sodium permeability changed with a relaxation time that was also shorter than the duration of the normal mode laser output. T-jumps observed during a hyperpolarization or at the resting potential showed no detectable conductance change. When a T-jump immediately preceded a voltage clamp pulse the technique was then used to investigate the effect of changes in the steady-state temperature on the ionic conductances. It was found that the magnitude of the change in membrane current due to a T-clamp was directly related to the level of cathodal polarization.

Animals↗
PubMed1972

Voltage clamp experiments of single muscle fibers of Rana pipiens.

A voltage clamp for single muscle fibers has been developed. Stability of the system was achieved when an artificial node was created by enclosing a single muscle fiber in a petroleum jelly seal which served as an analogue of the myelin sheath. Typical voltage clamp records were obtained with large inward transient currents followed by a delayed rectification of the outward currents. These currents looked qualitatively similar when the transverse tubular system was destroyed. Errors in current measurement, especially those due to anomalous rectification, are discussed.

Action Potentials↗
PubMed1969

Anion permeability of frog skeletal muscle.

Unidirectional chloride effluxes from small bundles of muscle fibers were measured under equilibrium conditions. It was found that chloride effluxes are described by the constant field theory with a chloride permeability constant, P(cl), which is independent of the chloride concentration and the membrane potential. The value of P(cl) at neutral pH was found to be 5 x 10(-6) cm/sec. Chloride movements were markedly depressed at low pH and increased at high pH. It is concluded that chloride fluxes are independent of each other over a wide pH range. The effect of nitrate on the chloride effluxes was measured. It was found that both external and internal nitrate alone reduced the chloride efflux with the external nitrate appearing more effective than internal nitrate due to the nonequilibrium nature of the experimental conditions. Under equilibrium conditions the reduction of the chloride efflux by nitrate was greater than the external nitrate effect, both of which were dependent on the relative proportion of nitrate in the bathing solution. These results are consistent with the hypothesis that the inhibition of the chloride movements by nitrate is essentially symmetrical with regard to the inside and outside surfaces of the muscle membranes. The relative action of nitrate on the chloride efflux was independent of the external pH despite marked changes in the absolute values of the fluxes measured.

Animals↗
PubMed1967

Membrane currents at large positive internal potentials in single myelinated nerve fibres of Rana pipiens.

1. A voltage clamp for single myelinated nerve fibres was developed from commercially available operational amplifiers.2. Under voltage clamp conditions steady-state currents were measured. The currents reached a maximum value at about E = + 100 mV. Currents for greater potentials decreased.3. The preceding polarization markedly affected the magnitude of the delayed current at high cathodal potentials; however, the currents continued to reach maximum values.4. As predicted by the constant field theory, currents at high cathodal polarizations were essentially independent of the external potassium concentration. Also, these currents were independent of the external calcium concentration.5. Two pulse voltage clamp experiments showed that instantaneous outward currents did not reach a limiting value. The limiting steady-state current was reached with an exponential time constant of about 1 msec.

Animals↗
PubMedDate not supplied

Reduced placental perfusion causes an increase in maternal serum leptin.

OBJECTIVE: We tested the hypothesis that the inadequately perfused placenta increases production of leptin, which can be detected in maternal serum. STUDY DESIGN: Sprague-Dawley rats (n=13), on day 14 of gestation, had placement of clips on the aorta and the ovarian arteries providing 35 per cent occlusion of the vessels. Eight rats had sham surgery and 14 rats served as non-surgical controls. All animals were sacrificed on day 19 of gestation. Maternal serum was obtained, and pups and placentae were weighed. RESULTS: Both placental weights and pup weights were reduced due to reduced uterine perfusion and were negatively correlated with maternal serum leptin (P=0.018 and 0.028, respectively). Maternal serum leptin was increased in the treatment group (2.21 ng/ml+/-64 ng/ml) compared to controls (1.66 ng/ml+/-38 ng/ml) (P=0.031). CONCLUSIONS: Our findings suggest that reduced placental perfusion results in an increase in maternal serum leptin. Further investigation is needed to determine if maternal serum leptin may be useful in identifying pregnancies with uteroplacental insufficiency.

Animals↗
PubMedDate not supplied

Parameter estimation methods for single neuron models.

With the advancement in computer technology, it has become possible to fit complex models to neuronal data. In this work, we test how two methods can estimate parameters of simple neuron models (passive soma) to more complex ones (neuron with one dendritic cylinder and two active conductances). The first method uses classical voltage traces resulting from current pulses injection (time domain), while the second uses measures of the neuron's response to sinusoidal stimuli (frequency domain). Both methods estimate correctly the parameters in all cases studied. However, the time-domain method is slower and more prone to estimation errors in the cable parameters than the frequency-domain method. Because with noisy data the goodness of fit does not distinguish between different solutions, we suggest that running the estimation procedure a large number of times might help find a good solution and can provide information about the interactions between parameters. Also, because the formulation used for the model's response in the frequency domain is analytical, one can derive a local sensitivity analysis for each parameter. This analysis indicates how well a parameter is likely to be estimated and helps choose an optimal stimulation protocol. Finally, the tests suggest a strategy for fitting single-cell models using the two methods examined.

Animals↗
PubMedDate not supplied

When betamethasone and dexamethasone are unavailable: hydrocortisone.

OBJECTIVE: To review the literature on alternatives to betamethasone and dexamethasone for enhancement of fetal lung maturity. STUDY DESIGN: A medline search was conducted from 1966 to the present. Trials dealing with enhancement of fetal lung maturity using modalities other than betamethasone or dexamethasone were reviewed. RESULTS: Eight studies met inclusion criteria. Excluding betamethasone and dexamethasone, the most frequently studied glucocorticoids, for fetal lung maturation, are methylprednisolone and hydrocortisone. Methylprednisolone does not cross the placenta. Two grams of hydrocortisone has been shown to improve indices of fetal lung maturity (i.e., L/S ratio) and to improve fetal outcomes compared to no treatment. CONCLUSION: There is limited information about alternatives to betamethasone and dexamethasone for the enhancement of fetal lung maturity in women at risk of preterm delivery. In the absence of these two preferred drugs, hydrocortisone can be given at a dose of 500 mg intravenously every 12 hours for four doses for this indication.

Anti-Inflammatory Agents↗
PubMedDate not supplied

Quantitation of DNA in buccal cell samples collected in epidemiological studies.

Buccal cell samples are increasingly used in epidemiological studies as a source of genomic DNA. The accurate and precise quantitation of human DNA is critical for the optimal use of these samples. However, it is complicated by the presence of bacterial DNA and wide inter-individual variation in DNA concentration from buccal cell collections. The paper evaluated the use of ultraviolet light (UV) spectroscopy, Höechst (H33258) and PicoGreen as measures of total DNA, and real-time quantitative polymerase chain reaction (PCR) as a measure of human amplifiable DNA in buccal samples. Using serially diluted white blood cell DNA samples (at a concentration range of 300 to 0.5 ng microl-1), UV spectroscopy showed the largest bias, followed by Höechst, especially for low concentrations. PicoGreen and real-time PCR provided the most accurate and precise estimates across the range of concentrations evaluated, although an increase in bias with decreasing concentrations was observed. The ratio of real-time PCR to PicoGreen provided a reasonable estimate of the percentage of human DNA in samples containing known mixtures of human and bacterial DNA. Quantification of buccal DNA from samples collected in a breast cancer case-control study by PicoGreen and real-time PCR indicated that cytobrush and mouthwash DNA samples contain similar percentages of human amplifiable DNA. Real-time PCR is recommended for the quantification of buccal cell DNA in epidemiological studies since it provides precise estimates of human amplifiable DNA across the wide range of DNA concentrations commonly observed in buccal cell DNA samples.

Cheek↗
PubMedDate not supplied

Novel biomarkers of genetic damage in humans: use of fluorescence in situ hybridization to detect aneuploidy and micronuclei in exfoliated cells.

Here we describe new techniques that employ fluorescence in situ hybridization (FISH) with centromeric and chromosome-specific DNA probes to detect aneuploidy and micronucleus formation in exfoliated human epithelial cells. Micronuclei arise from chromosome breakage or lagging, which results in chromosome fragments and whole chromosomes being left outside of the main nucleus at telophase. By using a centromeric DNA probe to detect the presence of whole chromosomes in micronuclei and propidium iodide as a general DNA stain in exfoliated nasal, buccal, and bladder cells, we have developed a new fluorescent method that can detect micronuclei and determine the mechanism of formation. The new fluorescent technique gave results that were very similar to those obtained with the standard Feulgen-fast green method. The spontaneous levels of micronuclei in healthy volunteers were buccal, 0.13%, nasal, 0.21%, and urothelial, 0.07%, in approximately 1500 cells per data point. These values are lower than that found in cultured lymphocytes, 0.4-0.8%. Approximately 50% of the exfoliated cell micronuclei contained whole chromosomes (centromeric DNA). FISH was also used to detect aneuploidy in exfoliated buccal and bladder cells. A DNA probe specific for chromosome 9 was used. Average frequencies for 0, 1, 2, 3, and 4 hybridization regions were 4.8, 9.3, 84.8, 0.8, and 0.3% for urothelial cells and 8.2, 9.9, 80.1, 1.4, and 0.4% for buccal cells. The estimated frequency of aneuploidy in exfoliated cells is similar to that found in human lymphocytes analyzed by FISH with the same probe for chromosome 9. These techniques are potentially useful for epidemiological studies of exposed populations and are currently being applied in our laboratory for studies of arsenic- and formaldehyde-exposed populations.

Adult↗