SEARCH · PubMed Health

Results for “Distance--determinants”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources

PubMed2005

Oxygen delivery to the fish eye: root effect as crucial factor for elevated retinal PO2.

Although the retina has one of the highest metabolic rates among tissues, certain teleost fishes lack any vascular supply to this organ which, in combination with the overall thickness of the organ, results in extremely long diffusion distances. As the only way to compensate for these obstacles, oxygen partial pressure (PO2) in the eyes of such fish is elevated far above atmospheric values. Although not supported by any direct evidence, the enhancement of PO2 is considered to be related to the Root effect, the release upon acidification of Hb-bound O2 into physical dissolution, possibly supported by counter-current multiplication similar to the loop of Henle. The present study evaluates the magnitude of intraocular PO2 enhancement under tightly controlled physiological conditions, to directly confirm the involvement of the Root effect on intraocular PO2 in the retina of rainbow trout Oncorhynchus mykiss. Intraocular PO2 was determined with special polarographic microelectrodes inserted into the eye. PO2 profiles established in vivo by driving electrodes through the entire retina yielded average PO2 values between 10 mmHg (1.3 kPa) at the inner retinal surface and 382 mmHg (50.9 kPa) close to the outer retinal limit (Bruch's membrane). According to estimates on the basis of the diffusion distances determined from sections of the retina (approximately 436 microm at the site of PO2 measurement) and literature data on specific oxygen consumption, the in vivo determined values would be sufficient to cover the oxygen demand of the retina with some safety margin. For a clear and direct in-tissue-test as to the involvement of the Root effect, an isolated in vitro eye preparation was established in order to avoid the problem of indirect blood supply to the eye from the dorsal aorta only via the pseudobranch, a hemibranch thought to modulate blood composition before entry of the eye. Any humoral effects (e.g. catecholamines) were eliminated by perfusing isolated eyes successively with standardized red blood cell (RBC) suspensions in Ringer, using trout (with Root) and human (lacking any Root effect) RBC suspension. To optimize perfusate conditions for maximal Root effect, the Root effect of trout RBCs was determined in vitro via graded acidification of individual samples equilibrated with standardized gas mixtures. During perfusion with trout RBC, PO2 at the outer retinal limit was 99 mmHg (13.2 kPa), but fell by a factor of 3.3 upon perfusion with human RBC in spite of higher total oxygen content (TO2 2.8 for trout vs 3.9 mmol l-1 for human RBC). Upon reperfusion with trout RBC, PO2 was restored immediately to the original value. This regularly observed pattern indicated a highly significant difference (P=0.003) between perfusion with trout (with Root effect; high retinal PO2) and perfusion with human (no Root effect; low retinal PO2) RBC suspension, thus clearly demonstrating that the Root effect is directly involved and a crucial prerequisite for the enhancement of PO2 in the retina of the teleost eye.

Animals↗

PubMed1999

Active electrolocation of objects in weakly electric fish

Weakly electric fish produce electric signals (electric organ discharges, EODs) with a specialised electric organ creating an electric field around their body. Objects within this field alter the EOD-induced current at epidermal electroreceptor organs, which are distributed over almost the entire body surface. The detection, localisation and analysis of objects performed by monitoring self-produced electric signals is called active electrolocation. Electric fish employ active electrolocation to detect objects that are less than 12 cm away and have electric properties that are different from those of the surrounding water. Within this range, the mormyrid Gnathonemus petersii can also perceive the distance of objects. Depth perception is independent of object parameters such as size, shape and material. The mechanism for distance determination through electrolocation involves calculating the ratio between two parameters of the electric image that the object projects onto the fish's skin. Electric fish can not only locate objects but can also analyse their electrical properties. Fish are informed about object impedance by measuring local amplitude changes at their receptor organs evoked by an object. In addition, all electric fish studied so far can independently determine the capacitative and resistive components of objects that possess complex impedances. This ability allows the fish to discriminate between living and non-living matter, because capacitance is a property of living organisms. African mormyrids and South American gymnotiforms use different mechanisms for capacitance detection. Mormyrids detect capacitance-evoked EOD waveform distortions, whereas gymnotiforms perform time measurements. Gymnotiforms measure the temporal phase shift of their EODs induced at body parts close to the object relative to unaffected body parts further away.

Journal Article↗

PubMed1981

Estimation of inter-electrode distance for body surface mapping: application of Fourier analysis to potential distribution due to the epicardial breakthrough.

For the purpose of determining an appropriate distance of lead points for constructing body surface maps, Fourier analysis was performed on potential distribution reflecting the epicardial breakthrough, and inter-electrode distance necessary for sampling of harmonics contributing to the body surface potential distribution was determined by application of sampling theorem. Potential distribution was simultaneously recorded with an interval of 4 mm for 250 msec along the vertical (head to foot) and horizontal (right to left) line crossing a second-minimum appearing on the chest surface of a healthy adult, and the data obtained from 9.6 cm along the respective lines underwent Fourier transform. Relative contribution of the second harmonics to the original wave forms increased with time lapse after QRS initiation, in accordance with reductions of the first harmonics component, and attained the maximum (32.5% of total power spectrum without d-c component) at the instant of occurrence of the second-minimum. A similar tendency was observed among higher harmonics, but their contribution was comparatively low (within 10%). Inter-electrode distance determined by sampling theorem was 4.8 cm for the first harmonics and 2.4 cm for the second harmonics. In conclusion it is proposed that placement of electrodes with an inter-electrode distance of 2.4 cm is necessary for acquiring clinically important data on the epicardial breakthrough.

Electrocardiography↗

PubMed2005

Perceptual and neural olfactory similarity in honeybees.

The question of whether or not neural activity patterns recorded in the olfactory centres of the brain correspond to olfactory perceptual measures remains unanswered. To address this question, we studied olfaction in honeybees Apis mellifera using the olfactory conditioning of the proboscis extension response. We conditioned bees to odours and tested generalisation responses to different odours. Sixteen odours were used, which varied both in their functional group (primary and secondary alcohols, aldehydes and ketones) and in their carbon-chain length (from six to nine carbons). The results obtained by presentation of a total of 16 x 16 odour pairs show that (i) all odorants presented could be learned, although acquisition was lower for short-chain ketones; (ii) generalisation varied depending both on the functional group and the carbon-chain length of odours trained; higher generalisation was found between long-chain than between short-chain molecules and between groups such as primary and secondary alcohols; (iii) for some odour pairs, cross-generalisation between odorants was asymmetric; (iv) a putative olfactory space could be defined for the honeybee with functional group and carbon-chain length as inner dimensions; (v) perceptual distances in such a space correlate well with physiological distances determined from optophysiological recordings of antennal lobe activity. We conclude that functional group and carbon-chain length are inner dimensions of the honeybee olfactory space and that neural activity in the antennal lobe reflects the perceptual quality of odours.

Afferent Pathways↗

PubMed2004

Molecular modeling of nearly full-length ErbB2 receptor.

Members of the epidermal growth factor receptor family play important roles in various cellular processes, both in physiological and in pathological conditions. Dimerization and autophosphorylation of these receptor tyrosine kinases are key events of signal transduction. Details of the molecular events of the signaling are not entirely known. To facilitate the understanding of receptor structure and function at the molecular level, a molecular model was built for the nearly full-length ErbB2 dimer. Modeling was based on the x-ray or nuclear-magnetic resonance structures of extracellular, transmembrane, and intracellular domains. The extracellular domain was positioned above the cell membrane based on the distance determined from experimentally measured fluorescence resonance energy transfer. Favorable dimerization interactions are predicted for the extracellular, transmembrane, and protein kinase domains in the model of a nearly full-length dimer of ErbB2, which may act in a coordinated fashion in ErbB2 homodimerization, and also in heterodimers of ErbB2 with other members of the ErbB family.

Cell Line, Tumor↗

PubMed2005

Thymosin beta4 induces a conformational change in actin monomers.

Using fluorescence resonance energy transfer spectroscopy we demonstrate that thymosin beta(4) (tbeta(4)) binding induces spatial rearrangements within the small domain (subdomains 1 and 2) of actin monomers in solution. Tbeta(4) binding increases the distance between probes attached to Gln-41 and Cys-374 of actin by 2 A and decreases the distance between the purine base of bound ATP (epsilonATP) and Lys-61 by 1.9 A, whereas the distance between Cys-374 and Lys-61 is minimally affected. Distance determinations are consistent with tbeta(4) binding being coupled to a rotation of subdomain 2. By differential scanning calorimetry, tbeta(4) binding increases the cooperativity of ATP-actin monomer denaturation, consistent with conformational rearrangements in the tbeta(4)-actin complex. Changes in fluorescence resonance energy transfer are accompanied by marked reduction in solvent accessibility of the probe at Gln-41, suggesting it forms part of the binding interface. Tbeta(4) and cofilin compete for actin binding. Tbeta(4) concentrations that dissociate cofilin from actin do not dissociate the cofilin-DNase I-actin ternary complex, consistent with the DNase binding loop contributing to high-affinity tbeta(4)-binding. Our results favor a model where thymosin binding changes the average orientation of actin subdomain 2. The tbeta(4)-induced conformational change presumably accounts for the reduced rate of amide hydrogen exchange from actin monomers and may contribute to nucleotide-dependent, high affinity binding.

Acrylamide↗

PubMed1999

The effect of the Müller-Lyer illusion on map reading.

One important reason for studying visual illusions is that they can influence real-world perception as people interact with human-made displays. Three experiments examined how the Müller-Lyer illusion affects distance judgments and decision-making in the complex graphical context of a map by having subjects estimate the lengths of road segment lines framed by inward-going or outward-going wings in actual maps, in control displays that had the map context removed, and in simulated maps. The experiments showed that (1) outward-going wings led to higher distance estimates than did inward-going wings to the same extent both with and without the map context, (2) decisions based on distances determined from maps were affected by Müller-Lyer elements in the maps, and (3) map readers' measurement behavior influenced the effect of the Müller-Lyer elements in maps. The discussion focuses on how certain display manipulations and task manipulations affect the Müller-Lyer illusion. In addition, the discussion addresses the instances in which using a map might be affected by misestimation due to Müller-Lyer elements.

Adult↗

PubMed2002

Selective reaching: evidence for multiple frames of reference.

Students participated in 3 experiments investigating the use of environment- and action-centered reference frames in selective reaching. They pointed to a green target appearing either with or without a red distractor. Target-distractor distance was manipulated, and distractor interference (difference between distractor trials and no-distractor trials) was measured in reaction time, movement time, and movement endpoint. Target-distractor distance determined the dominant frame of reference. Small distances evoked an environment-centered framework that encoded targets within an external context. Large distances evoked an action-centered framework that encoded targets relative to the start position of the hand. Results support the hypothesis that the brain represents spatial information in multiple frames of reference, with the dominant frame of reference being dependent on the task demands.

Adolescent↗

PubMed1991

An interpretation of the effects of age on migration: Nordic migrants' choice of settlement in Sweden.

A model of the relationship between age and migration is developed and applied to data concerning migrants from other Scandinavian countries who settled in Sweden between 1968 and 1985. The author shows "how changes in Sweden's domestic economic conditions and distance determine the probability for settlement in any of its 24 provinces for migrants of different ages. The results show that in the integrated Nordic labor market, wages at destination do not explain differences in migrants' settlement behavior across ages. Instead they suggest that the major factors to explain the differences are the labor market situation for the different age groups and distance."

Age Factors↗

PubMed1992

Cuticular hydrocarbons, isoenzymes and behavior of three populations of Anopheles darlingi from Brazil.

Three populations of Anopheles darlingi were studied for cuticular hydrocarbons, isoenzymes and patterns of peak biting activity. Differences were found in specimens from Costa Marques, a malaria endemic area; Dourado, a site with a very exophilic population and Juturnaíba, located near the type locality. Twelve hour collections from sunset to sunrise showed that An. darlingi from Costa Marques had a bimodal biting activity profile with a major peak at sunset and a minor peak at sunrise. At Dourado, the pattern was trimodal, with peaks at both morning and evening periods of twilight and near midnight. The Juturnaíba population showed a slight increase in activity near 2000 and 0100 h. Nei's genetic distances, determined by isoenzyme electrophoresis between pairs of populations, were low (D < or = 0.049). Using discriminant analysis for the cuticular hydrocarbons, 92.4% of the specimens from Costa Marques, 91.2% of the specimens from Dourado and 61.3% from Juturnaíba were correctly identified. Cuticular hydrocarbon and isoenzyme results matched very well: the smaller the Nei's distance, the more misidentifications occurred in the jackknife estimator used in the cuticular hydrocarbon analysis. This is the first report of cuticular hydrocarbon analysis in combination with isoenzymes to investigate neotropical anopheline species.

Animals↗

PubMed1999

[Interatomic distances of molecule for orthohydrogen and parahydrogen].

The determination of rotational Raman spectra for hydrogen gas at 354.9, 587.4, 814.7 and 1035.1 cm(-1) by FT-Raman spectrometry is described in this paper. The Raman bands at 354.9 and 814.7 cm(-1) were assigned to rotational levels J = 0 --> J = 2 and J = 2 --> J = 4 for parahydrogen, and those at 587.4 and 1035.1 cm(-1) were assigned to rotational levels J = 1 --> J = 3 and J = 3 --> J = 5 for orthohydrogen. The interatomic distances determined for orthohydrogen and parahydrogen molecules with nonrigid rotator model are 75.03 and 74.98 pm, respectively.

English Abstract↗

PubMed1991

Arrangement of the substrates at the active site of brain pyridoxal kinase.

The distances between enzyme-bound paramagnetic CrATP (a stable, beta, gamma-bidentate complex of Cr3+ and ATP) at the active site of sheep brain pyridoxal kinase and the protons of bound inhibitor 4-dPyr (4-deoxypyridoxine) were determined in the ternary enzyme-CrATP.4-dPyr complex by measuring the paramagnetic effects of Cr3+ on the longitudinal relaxation rates (1/T1p) of the protons of 4-dPyr. The correlation time for the Cr(3+)-4-dPyr dipolar interaction on the enzyme was estimated as 1.59 ns by the frequency dependence of 1/T1p of water protons. Temperature dependence of 1/T1p values indicated the fast exchange of 4-dPyr from the paramagnetic enzyme.CrATP.4-dPyr complex; hence the measured 1/T1p values can be used for metalnucleus distance determinations. The distances from the Cr3+ of the enzyme-bound CrATP to the 2-methyl (7.19 A), 4-methyl (7.18 A), and H6 proton (6.18 A) of the 4-dPyr are too great to permit a direct coordination of any group from 4-dPyr. However, these distances can be built into a model in which phosphorus of the gamma-phosphoryl group of ATP is 4 A away from the oxygen atom of the 5-CH2OH group of the 4-dPyr. This suggests that phosphorylation of pyridoxal can occur via direct transfer of the phosphoryl group between the bound substrates at the active site of pyridoxal kinase.

Adenosine Triphosphate↗

PubMed1990

Identification of a beta-turn in the tertiary structure of a peptide fragment of the Alzheimer amyloid protein.

In an attempt to understand the three-dimensional structure of the Alzheimer amyloid protein, a fragment decapeptide was studied by nuclear magnetic resonance spectroscopy. Using two-dimensional techniques, protons close in space were identified and their interproton distances determined. These distances were then used as input data for distance geometry calculations. The resulting three-dimensional structures suggest the presence of a beta-turn in the C-terminus of the decapeptide.

Amino Acid Sequence↗

PubMed1989

Conformation of NAD+ bound to allosteric L-lactate dehydrogenase activated by chemical modification.

On modification of arginine residues with 2,3-butanedione, the Thermus caldophilus L-lactate dehydrogenase is converted to an activated form that is independent of an allosteric effector, fructose 1,6-bisphosphate (Fru-1,6-P2). The conformation of NAD+ bound to the modified enzyme in the absence of Fru-1,6-P2 was investigated by means of proton NMR, analyzing the time dependence of the transferred nuclear Overhauser effect (TRNOE) and TRNOE action spectra. The inter-proton distances determined on TRNOE analysis indicated that both the nicotinamide riboside moiety and the adenosine moiety of NAD+ were in the anti conformation, the ribose rings being in the C3'-endo form. This conformation was almost the same as that of NAD+ bound to the native enzyme-Fru-1,6-P2 complex, rather than that of NAD+ bound to the free native enzyme. These results suggest that the C3'-endo-anti form of the enzyme-bound NAD+ is essential for the activation of the T. caldophilus L-lactate dehydrogenase.

Allosteric Regulation↗

PubMed1985

Nuclear magnetic resonance studies of fructose 2,6-bisphosphate and adenosine 5'-monophosphate interaction with bovine liver fructose-1,6-biphosphatase.

1H and 31P nuclear magnetic resonance was used to investigate the interaction of AMP and fructose 2,6-bisphosphate (Fru-2,6-P2) with bovine liver fructose-1,6-bisphosphatase. Mn2+ bound to fructose-1,6-bisphosphatase was used as a paramagnetic probe to map the active and AMP allosteric sites of fructose-1,6-bisphosphatase. Distances between enzyme-bound Mn2+ and the phosphorus atoms at C-6 of fructose-6-P and alpha-methyl-D-fructofuranoside 1,6-bisphosphate were identical, and the enzyme-Mn to phosphorus distance determined for the C-6 phosphorus atom of Fru-2,6-P2 was very similar to these values. Likewise, the enzyme-Mn to phosphorus distances for Pi, the C-1 phosphorus atom of alpha-methyl-D-fructofuranoside 1,6-bisphosphate, and the C-2 phosphorus atom of Fru-2,6-P2 agreed within 0.5 A. The distance between enzyme-bound Mn2+ and the phosphorus atom of AMP was significantly shorter than the distances obtained for any of the aforementioned ligands, but the presence of Fru-2,6-P2 caused the enzyme-Mn to phosphorus distance for AMP to lengthen markedly. NMR line broadening of AMP protons was studied at various temperatures. The dissociation rate constant was found to be greater than 20 s-1. It was concluded that Fru-2,6-P2 strongly affects the interaction of AMP with fructose-1,6-bisphosphatase and that the sugar most likely acts at the active site of the enzyme.

Adenosine Monophosphate↗

PubMed1986

[Analysis of the reproducibility of conditions of intracavitary irradiation of patients with cervix cancer].

The paper is concerned with the results of an analysis of reproducibility of conditions for intracavitary irradiation of 20 cervical cancer patients using metracolpostat, a combined therapeutic endostat consisting of 3 tubes: the central one to introduce radiation sources into the cervical canal and cavity of the uterus and 2 lateral ones with ovoids to deliver the sources to the vaults of the vagina. Topometric investigations for each patient were performed 4 times: before the first session of fractionated intracavitary irradiation with high activity 252Cf sources using the ANET-B unit and after each session of irradiation. It was shown that discordances between distances from the central endostat to the right and left lateral ovoids determined during roentgenotopometric preparation of each patient and taken as a basis of dosimetric design, and discordances between these distances determined as a result of roentgenotopometric control after each laying, are a random value distributed according to the normal law.

Brachytherapy↗

PubMed1985

[Population genetics of taiga hunters-deer breeders. Characteristics of the prevalence of HLA system markers among the native population of Central Siberia].

The postulated peculiarities of distribution of the HLA antigens in the Evenk population of the Central Siberia indicate this population to be, on the whole, Mongoloid. Prolonged isolated existence of small inbred populations of the Evenks resulted in the number of specific HLA-complex features, such as poor antigen diversity, low level of heterozygosity. Non-homogeneity of gene frequencies was noted, the prevailing genes being A9, B40 with frequencies reaching 50%. Of the remaining alleles found in the Evenks A2, Aw19 in A locus, B5, B15, B17, B27, Bw35 in B locus and Cw2, Cw3, Cw4-in C locus are only widely spread. Similar heterozygosis levels and the HLA-system profiles draw the Evenks and the populations of American Indians and Eskimos closer to one another. On the basis of the fact that significant positive correlation exists between genetic and geographic distances determined for the Evenks and the native populations of America, genetic resemblance of these populations may be considered as evidence for their original relationship. Postulated closeness of native Central-Siberian populations to Americanoids, as regards HLA-system, makes it possible to consider formation of specific complex of HLA-system peculiarities in native American population in the light of their Siberian origin, for the first time.

Animal Husbandry↗

PubMed1984

Photometric oculometry. II. Measurement of axial ocular distances with slit-lamp microscopy. Clinical evaluation, and comparison with ultrasonography.

Photometric oculometry is a slit-lamp technique, which makes possible an estimation of intraocular axial distances and axial length. The technique is based on a transformation of a sagittal slit-lamp movement into intraocular axial distances when the slit-lamp focal plane is moved in the optical axis from retina to cornea. Determination of the axial length in 50 eyes (refractive range +4.75 to -5.25 D) showed that the axial length varied from 21.9 mm in hypermetropic eyes to 26.0 mm in myopic eyes, with the emmetropic eyes being approximately 24 mm. A comparison of intraocular axial distances determined by photometric oculometry and by ultrasonography on a small series of eyes showed no significant differences between the axial length, the length of the vitreous body, and the lens thickness, whereas a significant difference between the anterior chamber depth was observed (photometry giving slightly larger values than ultrasound).

Adult↗