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Biomedical subjects

G R Naylor

Publications and source records attributed to G R Naylor.

15 recordsLinked to original sources
PubMed1985

Donnan potentials in rabbit psoas muscle in rigor.

Collins and Edwards (1971, Am. J. Physiol., 221:1130-1133) have shown that a tissue potential can be measured with microelectrodes in glycerinated muscle and that this potential is consistent with a Donnan equilibrium of small ions due to the concentration of net fixed electric charge on the contractile proteins. This approach has been combined with x-ray and light diffraction measurements of the muscle lattice dimensions, and the data are used to determine the thick filament charge and thin filament charge under a variety of different conditions. The thick filament charge is a function of the bathing solution, in particular its pH and ionic composition. These parameters are important in determining the volume of the equilibrium lattice and possibly are involved in the contraction mechanism itself.

Animals↗
PubMed1985

Distribution of mass in relaxed frog skeletal muscle and its redistribution upon activation.

Five orders of equatorial reflection were recorded from both relaxed and fully activated intact frog sartorius muscle using synchrotron x-ray radiation. Electron density maps of the myofilament lattice in axial projection were calculated from the integrated intensities by Fourier synthesis, using all possible phase combinations. These maps were evaluated systematically in terms of their compatibility with electron microscopically and biochemically derived properties of the lattice structure and with the minimum wavelength principle. For the relaxed state, one phase combination emerged as most consistent with these constraints: it shows a thick filament with a compact core surrounded by an annular shell of density. The distribution of mass suggests that the S-2 moiety of the myosin molecule is an integral part of the thick-filament backbone and the S-1 moiety makes up the shell and is tilted or slewed around the backbone. For the active state, there are two feasible maps, which differ according to whether or not the activation process is associated with phase inversion in two of the reflections. Both maps represent patterns of redistribution of mass upon activation in which the thick-filament backbone is practically unaffected and there is movement of density from the annular shell towards the thin filaments. In addition to this outward radial flux of density from the thick-filament periphery, the pattern of net mass transfer involves a pronounced azimuthal component in both cases. The total net mass transfer is equivalent to approximately 20% (no phase change) or approximately 40% (with phase change) of the S-1 mass. From the observed systematic increase in peak widths of the higher orders, the size of the crystalline domain in the myofilament lattice in the relaxed sartorius is estimated to be greater than 650 nm and the variations in myofilament lattice spacing among different myofibrils to be about +/- 3%. Furthermore, in the activated state, the equilibrium positions of the myofilaments are no longer well ordered, but are distributed statistically about the lattice points with a standard deviation of approximately 3 nm.

Animals↗
PubMed1984

Structural studies of muscle during force development in various states.

Structural studies concerned with force generating mechanisms in striated muscle fibers in different states are described. The first study deals with fibers in the "rigor" state, where ATP is absent and all the myosin heads form cross-bridges with the actin-containing filaments. In this state large axial forces are developed when ionic strength is reduced to very low levels. At the same time, the fiber expands radially, as indicated by both X-ray diffraction and light microscopy. Comparison of the latter two measurements indicates that force is developed in part because of differences in the lateral expandability of different parts of the sarcomere. Thus, under these conditions, force appears to be modulated by factors that operate at the filament rather than the cross-bridge level. The second study deals with the location of the myosin heads in the relaxed state, and the mass movement that takes place when the fiber is physiologically activated. By using the intense X-ray source at the Stanford Synchrotron Radiation Laboratory, five equatorial reflections were recorded for both the relaxed and the activated state, and a spatial resolution of 100 A was obtained. Analysis of the data indicates that (1) in the resting state, myosin heads protrude out from the thick filaments and extend toward the thin filaments, and (2) upon activation, significant loss of mass occurs only in the region peripheral to the thick filament backbone through a movement that has a pronounced azimuthal component. The latter movement can be taken as the overall shift in myosin subfragment 1 during the cross-bridge cycle.

Actins↗
PubMed1984

A 16-month analysis of urinary tract infection in children.

Results of the examination of urine specimens with evidence of acute urinary tract infections from children aged 16 years and under in general practice were analysed during a period of 16 months. Infections were much commoner in girls than in boys, with Escherichia coli most frequently involved in both groups. Urinary tract infections caused by Proteus strains were predominantly associated with boys. Infections in girls showed a higher incidence at 3, 6 and 16 years of age. Possible reasons for these sex- and age-associated patterns of infection are discussed. It is suggested than an important factor in the prevention of urinary tract infections in young girls is proper supervision of school lavatories. The report illustrates how much useful information can be obtained from the analysis of diagnostic results based on a simple but thorough laboratory approach.

Adolescent↗
PubMed1983

Incubation period and other features of food-borne and water-borne outbreaks of typhoid fever in relation to pathogenesis and genetics of resistance.

Examination of the incubation period of typhoid fever, the attack rate, and the spread of the case-onset pattern in food-borne and water-borne outbreaks and in experimental infections indicates that typhoid fever arises when organisms invade the circulation by at least two mechanisms--as a result of either the net growth of invading organisms at an early stage or a breakdown in host cellular mechanisms later. The distribution of case-onset patterns suggests that a small number of genes, possibly a single gene, controls host resistance in the early phase. The occurrence of bimodal or even trimodal case-onset patterns in a population exposed to infection by a particular dose of organisms reveals differences in genetic resistance within the population.

Adolescent↗
PubMed1982

Average electrostatic potential between the filaments in striated muscle and its relation to a simple Donnan potential.

An approximate analytical solution to the Poisson-Boltzmann equation for a cylindrical particle was used to calculate the relationship between the charge on the filaments and the average electrostatic potential. Both thick and then filaments were considered in the muscle lattice with a filament charge ratio of 4 to 1. Comparing this with a similar relationship obtained using simple Donnan theory showed a discrepancy at high charge where the Poisson-Boltzmann equation leads to saturation of the average potential. However, using two separate experiments from the literature, we have shown that at pH 7.0 muscle must not be close to saturation and thus is in a region of the curve where the two approaches agree.

Animals↗
PubMed1982

Cross-bridge properties in the rigor state.

The inability of applied strain to affect the equatorial diffraction pattern of the rigor fiber indicates that the attachment angle of S1 to the actin filament is extremely stable. The effects of lattice spacing on fiber length (at constant force) and force (at constant length) indicate that the S1 moiety is connected to the surface of the myosin filament by a link that is between 3 and 12 nm in length, which is considerably less than 60 nm length that has been assumed previously.

Animals↗
PubMed1981

X-ray diffraction of strained muscle fibers in rigor.

The effect of strain on the equatorial x-ray diffraction pattern of glycerinated rabbit psoas fibers was studied in the rigor (ATP free) state. Strains between 30 and 100 A per half sarcomere, measured directly by laser diffraction, did not change the intensity ratio, (10)/ . (11). Because the intensity ratio depends on the distribution of mass within the myofilament lattice, the negative result indicates that strain does not change the angle of attachment of the subfragment 1 (S1) moiety of the myosin molecule to the actin filament. The effect of strain on the ordering of the actin filaments also was considered and judged to be negligible.

Actomyosin↗
PubMed1980

Technique for the cultural examination of urine using a single plate (the Macba plate).

This technique for the cultural examination of urine provides, within 24 hours, using a single Petri dish, the colonial appearance of any bacteria present on MacConkey agar and on blood agar, a rough colony count of the bacteria present, their sensitivity to four chemotherapeutic agents, isolated colonies from which further sensitivity tests can be done if necessary and the opportunity to scrutinize contaminating organisms that, even though present in only small numbers, may be of help in diagnostic problems.

Bacteriological Techniques↗
PubMed1980

Qualitative and quantitative methods of studying the effect of lipids on bacteria grown on the surface of solid culture media.

New qualitative and quantitative methods are described for the investigation of the antibacterial activity of lipids on solid media by the application of lipid-impregnated filter paper over a lawn of the organisms. The methods have been used to investigate the antibacterial activity of unsaturated fatty acids that are important in skin defence. Oleic and linoleic acids inhibited Streptococcus pyogenes markedly, Staphylococcus aureus and Staph epidermidis to a lesser extent and had no effect on Escherichia coli and Pseudomonas aeruginosa. The inhibition of growth of a strain of Str. pyogenes from a sore throat was greater than that of a strain from an outbreak of impetigo. Linoleic acid was a more potent inhibitor of bacterial growth than oleic acid, and with both acids inhibition was more pronounced under aerobic than under anaerobic conditions of incubation. The methods described could be applied in other fields such as pharmacology, horticulture and industry.

Bacteria↗
PubMed1978

A simple circuit for automatic continuous recording of microelectrode resitance.

Microelectrodes with tip diameters less than or equal to 0.5 micron used for intracellular recording sometimes give artefactual readings due to tip potentials. These appear to be caused by a change in the tip of the microelectrode upon impalement with a corresponding change in microelectrode resistance. A circuit is described which enables the resistance of the microelectrode to be continuously monitored throughout an experiment. The electrode is used as one half of a potential divider for an a.c. signal at 20 Hz with an amplitude of 20 mV. The other half of the potential divider is a 1000 Momega resistor. The a.c. signal across the microelectrode is approximately proportional to the microelectrode resistance in the range 0 --50 Momega. This signal is amplified, rectified and smoothed and then displayed on a chart recorder or other convenient meter.

Animals↗
PubMed1977

Corynebacterium haemolyticum infections in Cambridgeshire.

In the Cambridge area, 143 patients infected with Corynebacterium haemolyticum were found during the period May 1967 to December 1974. The pharynx was the commonest site of infection and 100 of the 137 pharyngeal infections were in patients aged between 15 and 25 years. Such patients usually had a sore throat; about half of them also had a maculopapular rash. The organism and the clinical features which we have come to regard as typical of this infection are briefly described.

Adolescent↗