The relationship between o.e.r., r.b.e. and number of fractions for X-ray- or neutron-induced skin damage.

The skin reactions in aerated and hypoxic mouse tails after single or fractionated doses of 250 kV X-rays or fast neutrons (6 MeV deuterons on beryllium) have been measured. The o.e.r. for one to sixteen fractions of X-rays remains constant, while that for one to ten fractions of neutrons decreases with increasing neutron fractionation and decreasing neutron dose/fraction. The o.e.r. for X-rays was 1.7, for single-neutron doses 1.4, and for ten fractions of neutrons 1.25. It was anticipated that the o.e.r. for neutron-induced damage would decrease further as neutron fractionation is increased because the contribution to damage from the highest LET components of dose, the alpha and heavy recoil particles, would increase relative to the lowe LET components. The r.b.e. values obtained for skin damage were higher at all neutron doses/fraction examined in this study on tails than all those previously obtained in studies on skin at other sites on four species. This may be due to the influence of hypoxia on the r.b.e. measurements in the mouse tail.     

The r.b.e. of fast fission neutrons (2 MeV) for chronic radiation damage of the large bowel of rats after single dose and fractionated irradiation

Late damage in the rectum of rats was studied after local irradiation with 2 MeV fast fission neutrons and the results were compared with those for 300 kV X-rays. A similarity between latency times, and between clinical, gross pathological and histological appearances of the rectal obstruction after the two types of radiation was observed. The r.b.e. evaluated from ED 50/200 days values was 1.8 for single doses, 2.1 for two fractions and 3 for five fractions and these are similar to r.b.e.s from other investigations of chronic intestinal radiation damage. Using linear quadratic analysis, a limiting r.b.e. of 5 was obtained. The beta-values are similar for both radiation qualities. Because of the high gamma-contamination (25 per cent) in the RENT I beam a possible correction of the r.b.e. for neutrons only, assuming interaction, is discussed.     

Comparisons of steady-state anisotropy of the plasma membrane of living cells with different probes

We have used an extended Perrin equation which was in agreement with literature data for steady-state anisotropy (rSS) for a wide variety of artificial and isolated biological membranes labeled with various probes (Van der Meer et al. (1986) Biochim. Biophys. Acta 854, 38-44 to obtain the static component (r infinity) for the intact plasma membranes of living cells. We show that lipid structural order parameters can be obtained for DPH and TMA-DPH in the plasma membranes of intact cells. We have examined the relationship between 'fractional limiting hindered anisotropy', r infinity/r0, which is related to the lipid structural order parameter, of DPH, TMA-DPH, DPHpPC, and a series of depth-dependent probes (n-(9-anthroyloxy) fatty acids, with n = 2-16), using data from 19 cell types. There was a linear relationship between r infinity/r0 values of DPH and TMA-DPH, but the relationship between either of these probes was non-linear with respect to DPHpPC or the series of fatty acid probes. The relationship between r infinity/r0 values of DPHpPC and the series of fatty acid probes was linear, suggesting that they not only undergo similar motions in the membrane, but also experience similar types of restriction to motion, a type which is different from that experienced by DPH and TMA-DPH. We show that for the plasma membranes of living cells, 'second degree' order parameters can be estimated for DPH and TMA-DPH, and propose that the parameter r infinity/r0, or the 'fractional limiting hindered anisotropy', analogous to a 'first degree' order parameter, can be estimated for DPHpPC and the depth-dependent fatty acid probes to evaluate the density of membrane packing.     

Conformation of the glycotripeptide repeating unit of antifreeze glycoprotein of polar fish as determined from the fully assigned proton n.m.r. spectrum

With its simple glycotripeptide repeating structure the antifreeze glycoprotein of polar fish may be an especially simple conformational mode for mucin glycoproteins with similar but more complex structures. The fully assigned proton n.m.r. spectrum confirms the anomeric configurations of the hexapyranosidic sugars of the side chains and the coupling constants of the alpha GalNAc and the beta Gal residues show both to be in the expected 4C1 chair conformation. The assignment of a single resonance for each proton of the (Ala-Thr-Ala)n repeat unit coupled with the observation of long range nuclear Overhauser effects (n.O.e.) implies a three-fold repeating conformation. The resonances of the two alanines are distinct and can be assigned to their correct positions in the peptide sequence by n.O.e. observed at the amide proton resonances on saturation of the alpha proton signals. The amide proton coupling constants of all three peptide residues are similar and imply a limited range of peptide backbone torsion angles, phi CN. The large n.O.e. which has been observed between the amide proton and the alpha proton of the residue preceding it in the sequence implies large positive values for the peptide dihedral angle, psi CC. Limits are placed on possible values of side chain dihedral angles by the observation of the coupling constant between the alpha and beta protons of the threonyl residue. The observation of n.O.e. between the anomeric proton of GalNAc and the threonyl side chain protons gives information on the conformation of the alpha glycosidic linkage between the disaccharide and the peptide. n.O.e. observed between the protons of the beta glycosidic linkage indicates the conformation of the disaccharide and the large amide proton coupling constant of the GalNAc residue shows a trans proton relationship. The spectroscopically derived data have been combined with conformational energy calculations to give a conformational model for antifreeze glycoprotein in which the hydrophobic surfaces of the disaccharide side chains are wrapped closely against a three-fold left handed helical peptide backbone. The hydrophilic sides of the disaccharides are aligned so that they may bind to the ice crystal face, which is perpendicular to the fast growth axis inhibiting normal crystal growth.     

Iron resorption and the effects of iron supplementation in blood donors]

Topical values for some haematological factors such as Hb and Ery as well as transferrin and ferritin were determined in 7 female blood donors and 8 male blood donors during the years of their work as blood donors. Subsequently, an iron resorption test was carried out which unexpectedly resulted in low rates of resorption ranging from 5.6% in men to 3.7% in women. After supplementing with vitaferro for 3 months the ferritin values which initially lay around the lower limiting value of 20 or 10 mg/l in men or women had doubled.     

A thermodynamic optimization analysis of a possible relation between the parameters that determine the energetics of muscle contraction in steady state.

Given the phenomenological relations for muscle's steady-state contraction and proper definitions of power p and efficiency eta, the behavior of these quantities is analysed in terms of the parameters that determine the energetics of the muscle, here denoted by s(o)and alpha. s(o)is proportional to the so-called maintenance heat, while alpha is the parameter that determines the curvature of the Hill's force-velocity curve. The dependence of the muscle's power and efficiency, averaged over the whole range of force the muscle can exert, on the parameters s(o)and alpha is studied. The average power p(avg)is a function only of alpha, and is a growing function that approaches 1/6 asymptotically as alpha goes to infinity. The average efficiency eta(avg)is a function of both alpha and s(o). With the value of s(o)fixed, the graph of the function eta(avg)(s(o), alpha) is a convex curve with a single maximum. The value and the position of this maximum point both depend on s(o). In the limit alpha-->0, s(o)-->0, eta(avg)tends to 1. The points (s(o), alpha(m)(s(o))), with alpha(m)(s(o)) the value of alpha that maximizes eta(avg)for a given s(o), are fitted by the curve alpha=s(o 1/2). This relation was experimentally found by A.V. Hill in his early studies of muscle energetics. Other experimental data are found to qualitatively satisfy the same relation. Although some dynamical microscopic models for muscle contraction, based upon Huxley's cross-bridge model, show that the same kinetic parameters control both the maintenance heat (s(o)) and the muscle's power output (alpha), we suggest that the exact relation between them has been reached due to the evolutive stresses that made individuals with equally powerful and more efficient muscles more suitable to reproduce.     

Chromosome aberrations induced in human lymphocytes by neutron irradiation.

In vitro dose--response curves of unstable chromosome aberrations in human lymphocytes have been obtained for neutron spectra of mean energies 0-7, 0-9, 7-6 and 14-7 MeV. The aberration yields have been fitted to the quadratic function Y = alphaD + betaD2, which is consistent with the single-track and two-track model of aberration formation. However with high-LET radiation, the linear component of yield, corresponding to damage caused by single tracks, predominants, and this term becomes more dominant with increasing LET, so that for fission spectrum neutrons the relationship is linear, Y = alphaD. At low doses, such as those recieved by radiation workers, limiting r.b.e. values between 13 and 47 are obtained relative to 60Co gamma-radiation. At higher doses, as used in radiotherapy, the values are much lower; ranging from 2-7 to 8 at 200 rad of equivalent gamma-radiation. Both sets of r.b.e. values correlate well with track-averaged LET but not with dose-averaged LET. When the numbers of cells without aberrations are plotted against radiation dose, curves are obtained which are similar in shape to those for conventional cell-survival experiments with comparable neutron spectra. The Do values obtained in the present study are close to those from other cell system.     

Modification of high LET radiation-induced damage and its repair in yeast by hypoxia.

The lethal response of a diploid yeast strain BZ34 to densely ionizing radiations from the reaction 10B(n, alpha)7 Li was studied. The values for relative biological effectiveness (r.b.e.) and oxygen enhancement ratio (o.e.r.) for this radiation compare favourably with the data obtained with charged particles on the same strain of yeast. Recovery from potentially lethal damage was also studied by post-irradiation holding under non-nutrient conditions. In order to understand the role of oxygen in the recovery process, the investigation covered the following treatment regimens: (a) aerobic irradiation and aerobic holding (A-A), (b) aerobic irradiation and hypoxic holding (A-H), (c) hypoxic irradiation and hypoxic holding (H-H) and (d) hypoxic irradiation and aerobic holding (H-A). It has been found that the presence of oxygen is essential for recovery from the damage induced by both gamma rays and high linear energy transfer (LET) radiations. The extent of recovery was larger for gamma-induced damage than for damage induced by high LET radiation (alpha + 7Li) for the A-A condition. In the H-H condition, while only a slight recovery was seen for gamma-induced damage, it was totally absent for high LET damage. For the modality A-H, it was found that there is not recovery from the sparsely ionising gamma radiation-induced damage. The implications of these results for the treatment of malignant tumours by radiotherapy are briefly discussed.     

Somatic aberration induction in Tradescantia occidentalis by neutrons, x- and gamma-radiations. II. Biological results, r.b.e. and o.e.r.

Biological results, including statistical features, are described for the irradiation of Tradescantia occidentalis with 250 kVp X-rays, cobalt-60 gamma-radiation and monoenergetic neutrons with energies between 0-08 and 15 MeV. The effect studied was that of the induction of pink sectors in the otherwise blue staminal hairs of the flowers at low doses of radiation. Statistical aspects of the results suggest that a fraction of the asynchronous cell population in the hairs is very sensitive to neutron radiation, but not necessarily to lower LET radiations. All the results were fitted by a least-squares method by polynomials of different degrees. Best fits to X- and gamma-ray data were provided by second-degree polynomials, and to the neutron data by either second- or third-degree polynomials. Limiting r.b.e. and o.e.r. values at low doses are derived. Some computed microdosimetric parameters are presented in comparison with the r.b.e. values. It is concluded that the effect studied is complex and may not provide a critical test of bio-physical theories of radiation effects.     

Network dynamics in nociceptive pathways assessed by the neuronal avalanche model

ABSTRACT: BACKGROUND: Traditional electroencephalography provides a critical assessment of pain responses. The perception of pain, however, may involve a series of signal transmission pathways in higher cortical function. Recent studies have shown that a mathematical method, the neuronal avalanche model, may be applied to evaluate higher-order network dynamics. The neuronal avalanche is a cascade of neuronal activity, the size distribution of which can be approximated by a power law relationship manifested by the slope of a straight line (i.e., the alpha value). We investigated whether the neuronal avalanche could be a useful index for nociceptive assessment. FINDINGS: Neuronal activities were recorded with 4 X 8 multichannel electrode arrays in the primary somatosensory cortex (S1) and anterior cingulate cortex (ACC). Under light anesthesia, peripheral pinch stimulation increased the slope of the alpha value in both the ACC and S1, whereas brush stimulation increased the alpha value only in the S1. The increase in alpha values was blocked in both regions under deep anesthesia. The increase in alpha values in the ACC induced by peripheral pinch stimulation was blocked by medial thalamic lesion, but the increase in alpha values in the S1 induced by brush and pinch stimulation was not affected. CONCLUSIONS: The neuronal avalanche model shows a critical state in the cortical network for noxious-related signal processing. The alpha value may provide an index of brain network activity that distinguishes the responses to somatic stimuli from the control state. These network dynamics may be valuable for the evaluation of acute nociceptive processes and may be applied to chronic pathological pain conditions.     

Relation of branching angles to optimality for four cost principles

The literature has suggested that branching angles depend on some principle of optimality. Most often cited are the minimization of lumen surface, volume, power and drag. The predicted angles depend on the principle applied, chi and alpha. Assuming flow o r chi, chi can be determined from r chi 0 = r chi 1 + r chi 2 when the radii of the parent (r0) major (r1) and minor (r2) daughters are known. The term alpha = r2/r1. Using different values for chi and alpha, we present graphs for the major and minor branching angles theta 1 and theta 2 and psi = theta 1 + theta 2 for each of the four optimization principles. Because psi is almost independent of alpha for values of chi and alpha found in 198 junctions taken from a human pulmonary artery, we are able to produce a plot of psi versus chi for each of the four principles on one graph. A junction can be provisionally classified as optimizing for a given principle if, knowing chi, the psi obs - psi pred is least for that principle. We find that this nomographic classification agrees almost perfectly with a previous classification based on a more exacting measure, the percent cost index I, where I = observed cost/minimum cost. We explain why this is to be expected in most but not all cases. First we generate a contoured percent cost surface of c = I - 100 around the optimally located junction, J, and superimpose a surface of equal angular deviations a = psi pred-psi obs. We find that c increases and a usually increases with distance from J as the actual junction moves along a straight line away from J. We then produce a plot of c versus a for two competing principles. A comparison of the principles demonstrates that, for most cases, a is smaller for the principle which has the smaller c value.     

Adding two components of radiosensitization by oxygen

It has been shown, or inferred, in various contexts that radiosensitization of cells by oxygen is the sum of two (or more) components. If the component sensitivities conform with the Alper and Howard-Flanders equation their sum cannot also conform, but, in practice, even the most meticulous experimental techniques will fail to reveal lack of conformity unless one of the component K values is at least nine times the other. Thus, despite the many results that have demonstrated conformity with the equation, the existence of at least two components may well be a general phenomenon. The killing of cells by radiation is attributable to a summation of lesions in different structures; different K values for the contributing components are therefore to be expected, since neither oxygen nor its competitors are likely to be present in uniform concentration in all elements of the cell nucleus. Provided the components have intrinsic values of o.e.r. greater than one, their addition results in sensitivity that increases monotonically with PO2, approaching asymptotically to the overall o.e.r. which is a weighted average of the component o.e.r.s. In a curve plotted with PO2 on a linear scale a point of inflection can occur only if one component o.e.r. has a value less than one (i.e. oxygen is protective for that component), and then only if relationships between the other parameters satisfy certain conditions. In cases in which points of inflection in the sensitivity curve has been observed these are unlikely to be accounted for by the addition of two components. The analysis of the consequences of adding two components of oxygen sensitization could apply also to chemical sensitization of hypoxic cells.     

The influence of oxygen on the survival and yield of DNA double-strand breaks in irradiated yeast cells.

Survival and induction of DNA double-strand breaks were studied in cells of Saccharomyces cerevisiae irradiated under oxic or anoxic conditions with 30 MeV electrons. A linear relationship between DNA double-strand breakage and dose was found in both cases. The o.e.r.-value for colony forming ability was found to be 1.9 +/- 0.2, whereas the o.e.r.-value for DNA double-strand breakage was 3.0 +/- 0.1. These results are not inconsistent with the idea that DNA double-strand breaks are involved in killing of yeast cells. The frequency of induction of DNA double-strand breaks was found to be 0.74 x 10(-11) double-strand breaks per g/mol per Gy when cells were irradiated under oxygen and 0.24 x 10(-11) double-strand breaks per g/mol per Gy under nitrogen.     

Mutation and inactivation of cultured mammalian cells exposed to beams of accelerated heavy ions. III. Human diploid fibroblasts.

The induction of inactivation and mutation to thioguanine-resistance in cultured human diploid fibroblasts was studied after exposure to ionising radiations with LET's in the range 20--470 keV micrometer-1. Unique r.b.e. values were obtained for inactivation and mutation induction with nine different qualities of radiation. The plot of r.b.e. verus LET gave humped curves for both endpoints; r.b.e. maxima were in the LET range 90--200 keV micrometer-1 but the maximum r.b.e. value for mutation induction was almost twice that for inactivation. The accuracy of estimates of mutation induction are discussed with regard to possible selective effects against mutants during post-irradiation growth.     

Radiosensitization of a mouse tumour by Ro 03-8799: acute and protracted administration

The nitroimidazole Ro 03-8799 has been tested as a sensitizer of hypoxic tumour cells, using regrowth delay of a mouse mammary carcinoma. This drug has a short biological half-life and has previously proved to be less promising in tumour experiments than was predicted from in vitro studies and from artificially hypoxic skin. The postulate that this might result from the delay in penetrating to poorly vascularized tumour regions has been tested by maintaining constant blood and tumour levels for 2 hours before irradiation, using an infusion pump. For equivalent gross tumour concentrations at the time of irradiation there was no significant difference in the radiosensitization achieved with a single dose or with prolonged administration. This indicates that slow penetration of the drug is not a problem.     

Survival of a mixture of cells of variable linear-quadratic sensitivity to radiation

The experimentally observed survival of a heterogeneous mixture of cells, each component of which obeys a different linear-quadratic survival response to ionizing radiation, is examined. It is shown that the survival relationship for the mixed population approaches a linear-quadratic form for low doses. The linear parameter of the low-dose relationship approached is equal to the average of the distribution of values of the linear parameter (alpha(i)) of the various components of the mixture. The quadratic parameter of the low-dose relationship approached is equal to the average of the distribution of values of the quadratic parameter (beta(i)) of the various components of the mixture minus one-half the variance of the distribution of the values of alpha(i). A numerical example of the survival expected for an exponentially growing population of Chinese hamster V79 cells is presented. From this it can be appreciated that the apparent value of the alpha and beta parameters obtained by fitting an experimentally obtained survival curve will depend on the range of doses over which survival is determined. The apparent value of beta is decreased at higher doses, producing a straightening of the survival curve to approach the exponential decrease in survival commonly observed for the terminal high-dose portion of survival curves. Apparent exponential survival at high doses is not inconsistent with linear-quadratic survival and may not indicate a multitarget or other mechanism of cell killing.     

Membrane association and conformational change of palmitoylated G(o)alpha

Bovine brain G(o)alpha was specifically palmitoylated in vitro. The apparent dissociation constant for depalmitoylated G(o)alpha (dG(o)alpha) was 0.273 microM, while that for palmitoylated G(o)alpha (pG(o)alpha) was 5.77 nM. The dissociation rate constant (K(21)) and dissociation half-life for dG(o)alpha were 8.4x10(-4) min and 825 min respectively, while no significant dissociation of pG(o)alpha was detected. The limiting membrane insertion pressures for pG(o)alpha and dG(o)alpha were 44.4 mN/m and 41.3 mN/m respectively. These data suggested that palmitoylation facilitated the membrane association of G(o)alpha. Conformational changes of dG(o)alpha and pG(o)alpha detected by monitoring fluorescence spectra and fluorescence quenching were significantly different after they were associated with the membrane. It was suggested that conformational changes of G(o)alpha upon membrane association might be related to regulation of G(o)alpha signaling by palmitoylation.     

Interaction of protein with a self-associating ligand. Deviation from a hyperbolic binding curve and the appearance of apparent co-operativity in the Scatchard plot

We derived a general formula to analyze a binding system in which a ligand self-associates, in terms of experimentally determinable quantities, i.e. r, the average number of bound ligands per protein molecule, and Lft, the total free ligand concentration, which are expressed as a ligand monomer unit. The limiting behaviors of the Scatchard plot (r/Lft vs r plot), that is, the intercepts on the r-axis and the r/Lft-axis, and the limiting slopes, are generally given. Three models that may be encountered are considered in detail. Numerical examples are also presented to illustrate how the self-association of a ligand affects the binding curves. The ligand self-association alone can cause deviation of the profile of the binding curve (r vs Lft plot) from a hyperbola, resulting in a nonlinear Scatchard plot. Therefore, analysis of the binding data without consideration of ligand self-association may lead to erroneous conclusions as to the numbers and classes of binding sites, co-operativity among the sites and binding parameter values.