FC Changes Research Articles

Increase in electromyogram low-frequency power in nonfatigued contracting skeletal muscle.

We studied the relationship between changing elbow joint angle and the power spectral density of the biceps brachii muscle electromyogram (EMG) during submaximal isometric contractions. For this purpose, we recorded the EMG of the biceps brachii muscle with surface electrodes in 13 subjects. Each subject held a 2.8-kg weight and contracted the biceps isometrically for 30 s at one of two lengths. The length of the muscle was changed by flexing the forearm toward the upper arm to form an angle of 135 degrees (L1) or 45 degrees (L2). We found that the mean centroid frequency (fc) of the EMG power spectral density was 26% lower at L1 than at L2 (P less than 0.01). For each subject there was no significant change in fc during the isometric contraction at either angle. In addition, in nine subjects who sustained fatiguing contractions of the biceps with a 6-kg load, fc decreased by 15% (P less than 0.025). These data suggest that a change in the length at which a muscle contracts isometrically can alter or induce indirectly an alteration in the frequency content of its EMG. This finding may have important implications for the assessment of respiratory muscle EMG especially during loaded breathing.

Changes in diaphragmatic EMG spectra during hyperpneic loads

Changes in electromyographic (EMG) activity of the diaphragm were examined in human subjects during different levels of voluntary hyperpnea. Diaphragmatic EMG was recorded using both surface and esophageal electrodes. The power spectra density (PSD) of the EMG signal was calculated and characterized by the high frequency to low frequency (H/L) ratio and by the centroid frequency (Fc). During high levels of voluntary hyperpnea, a significant decrease in both the H/L ratio and Fc occurred, which was similar in diaphragmatic EMG recorded by either surface or esophageal electrodes. This similarity in EMG spectral changes suggested thath when diaphragmatic EMG was recorded usuing surface electrodes, there was only minimal contamination from the activity of other chest wall muscles. Changes in EMG Fc were detected during levels of hyperpnea which could be readily sustained. Thus, diaphragmatic EMG spectral changes were not characteristic of imminent ventilaltory failure ( i.e., an inability to sustain a target level of ventilation). On contrast, significant changes in EMG H/L ratio were observed only during hyperpneic loads which could not be sustained. This difference in sensitivity between the Fc and H/L ratio was due to the increased variability of H/L ratio and suggests that the H/L ratio may fail to detect small but significant shifts in EMG spectra. The relationship between the rate of decrease in EMG Fc and the level of hyperpnea was not statistically significant. We conclude that diaphragmatic EMG spectral changes do occur during hyperpneic loads, but we question the specificity of using diaphragmatic EMG spectral changes in predicting ventilatory failure.

Fc and C3b receptor changes on mouse peritoneal leucocytes following stimulation with an extract of ascaris suum

Changes in IgG-Fc and IgM-C3b receptors of mouse peritoneal leucocytes after in vivo stimulation with Ascaris suum adult extract were studied. Erythrocyte IgG-Fc rosettes were found to initially be decreased with A. suum stimulated neutrophils, eosinophils and macrophages in comparison with nonstimulated cells. IgG-Fc rosettes then increased with time and remained high for a 60 min exposure time. IgM-C3b rosette formation was lower with A. suum stimulated leucocytes throughout 60 min of exposure and dropped off dramatically after 30 min. Unstimulated leucocytes formed IgM-C3b rosettes sooner and maintained them at higher levels for a longer period of time than stimulated cells.

Dispersive ordering results

A distribution F is less dispersed than a distribution G if for all . We generalize a characterization of dispersive ordering of Shaked (1982) concerning sign changes of Fc – G, where Fc is a translate of F. We then use this generalization plus total positivity to develop a simple proof of a characterization of dispersive distributions due to Lewis and Thompson (1981); a distribution H is dispersive if

Dispersive ordering results

A distribution F is less dispersed than a distribution G if for all .We generalize a characterization of dispersive ordering of Shaked (1982) concerning sign changes of Fc – G, where Fc is a translate of F. We then use this generalization plus total positivity to develop a simple proof of a characterization of dispersive distributions due to Lewis and Thompson (1981); a distribution H is dispersive if

Human B-lymphocyte maturation sequence revealed by TPA-induced differentiation of leukaemic cells

Normal human B cells and leukaemic B-cell populations in common-type CLL undergo sequential shifts in proportions of the three B-cell subsets, defined by expression of mouse erythrocyte receptors R 1 and R 2, during TPA-induced differentiation to plasmacytoid cells in vitro, suggesting that the B-cell differentiation pathway is R 1 +R 2 + → R 1 -R 2 + → R 1 -R 2 - → immature plasmacyte. Maturation of the less common type of CLL with a predominance of R 1 -R 1 + type cell was in agreement with this model. Changes in Fc γ, Fc μ and C ′ receptors were also observed during maturation. A model of human B-cell maturation is presented on which common sites of blockage in leukaemia can be located.

Solubilization sites in micellar sodium octylsulphate solutions by ultrasonic spectroscopy

Relaxation frequencies fc and amplitudes A were measured ultrasonically over the 3.5–52.5 MHz range at 25 °C for the fast exchange of monomer between micelles and bulk solution in micellar sodium octylsulfate solutions with solubihzates present in small amounts. The additives were cyclohexane, pyridine-2-azo-p-dimethylaniline (PADA), benzene, toluene, and p-xylene. Only cyclohexane produced no changes in fc or A. The variations in the relaxational parameters suggested that cyclohexane was situated within the micellar core and PADA, primarily in the surface region of the micelle. Benzene and toluene were adsorbed in minute quantities into the micelle surface but, with additive concentrations beyond a few molecules per micelle, were found principally in the micellar core. Toluene, along with p-xylene, showed an initial dip in fc that may indicate that the first few molecules of these additives were incorporated into the palisade layer of the micelle.

Internal motions of antibody molecules.

ANTIBODY molecules of the IgG class are composed of three covalently linked regions1,2. Two of these (designated Fab) are identical and bind antigen; the third (Fc) has been identified as the site of antibody effector functions (for example, complement fixation), which are activated by antigen binding3. There is evidence that the binding of antigen to the Fab region induces an allosteric transition in IgG and that this transition may be a step in the effector activation process4. The findings of Pecht et al.5 indicate that for complement fixation both Fab regions must bind antigen, even though binding to one induces some conformational change in Fc. Binding of hapten does not lead to complement fixation in general, but some exceptions to this rule are known6. The interchain disulphide bridges must be intact for Fab ligand binding to have a productive effect on the Fc region7,8. Both the Fab and Fc regions have a domain structure; each consists of a pair of compact lobes covalently linked by strands of polypeptide chains9. A schematic diagram of the connectivity of the IgG lobes is given by Padlan10. One of the fundamental questions involved in antibody function is the nature of the mechanism by which binding of antigen to the Fab regions affects the Fc region. Huber et al. have recently outlined a possible allosteric model for the activation step on the basis of X-ray and other data9. In this note we use simple diffusion arguments to estimate the characteristic times associated with the Huber proposal. Since the analysis deals only with the relative motion of the IgG domains, it is possible that slower intradomain structural changes are also involved in the activation process; if so, the estimated characteristic times would be lower bounds for the activation time. The role of conformational transitions in effector function activation is still in dispute11, but we note that the diffusional model may be useful for analysing other dynamical phenomena in immunoglobulins, such as their fluorescence depolarisation behaviour12–14.