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PubMed1991

Priming of calcium mobilization in human neutrophils by granulocyte-macrophage colony-stimulating factor: evidence for an involvement of phospholipase D-derived phosphatidic acid.

Human neutrophils pre-incubated with granulocyte-macrophage-colony-stimulating factor (GM-CSF) exhibit an enhanced mobilization of calcium in response to secondary stimuli such as chemotactic factors. The mechanisms underlying this priming effect of GM-CSF were examined. It was first demonstrated that the additional calcium mobilized by chemotactic factors in GM-CSF-treated cells was derived from intracellular stores and was associated neither with an increased permeability to calcium nor with production of inositol 1,4,5-trisphosphate. These results indicated that GM-CSF called upon a novel mechanism in order to enhance the mobilization of calcium in human neutrophils. The growth factor has recently been shown to prime phospholipase D leading to an enhanced activation by chemotactic factors and an augmented production of phosphatidic acid. Furthermore the ability of exogenous phosphatidic acid to mobilize calcium in cell types other than neutrophils has been previously demonstrated. Therefore, we examined the potential involvement of phospholipase D in the priming of the calcium response by GM-CSF in human neutrophils. Inhibition of the production of the fMet-Leu-Phe-stimulated production of phosphatidic acid by ethanol or wortmannin had only marginal effects on the concurrent mobilization of calcium. However, the priming of the mobilization of calcium by GM-CSF was greatly decreased in cells treated with either ethanol or wortmannin. These results provide strong support for the hypothesis that the production of phosphatidic acid, which is enhanced in GM-CSF-treated cells, is linked to an increased mobilization of intracellular calcium. These results may have relevance to the mechanism of action of GM-CSF in mature haematopoeitic cells as well to the mitogenic activity of other growth factors.

Adult↗

PubMed2006

The effects of mobile phone use on pedestrian crossing behaviour at signalized and unsignalized intersections.

Research amongst drivers suggests that pedestrians using mobile telephones may behave riskily while crossing the road, and casual observation suggests concerning levels of pedestrian mobile-use. An observational field survey of 270 females and 276 males was conducted to compare the safety of crossing behaviours for pedestrians using, versus not using, a mobile phone. Amongst females, pedestrians who crossed while talking on a mobile phone crossed more slowly, and were less likely to look at traffic before starting to cross, to wait for traffic to stop, or to look at traffic while crossing, compared to matched controls. For males, pedestrians who crossed while talking on a mobile phone crossed more slowly at unsignalized crossings. These effects suggest that talking on a mobile phone is associated with cognitive distraction that may undermine pedestrian safety. Messages explicitly suggesting techniques for avoiding mobile-use while road crossing may benefit pedestrian safety.

Accidents, Traffic↗

PubMed2005

Identifying the relationship among mental status, functional independence and mobility level in Turkish institutionalized elderly: gender differences.

The purpose of this study was to examine gender differences in older people living at a rest home in terms of functional independence, mental status and mobility level and to describe the relationship among the three outcome variables. One hundred and thirty-three elderly people (60 women, 73 men), aged 65 years and above were included in the study. The average age was 75.3 +/- 6.7 years (range, 65-90 years). Mental status was assessed using the Hodkinson Mental Test (HMT). Functional independence was measured using Functional Independence Measurement (FIM). Mobility level was evaluated using the Rivermead Mobility Index (RMI). Elderly women had lower scores regarding all the outcome variables when compared to older men. The older men had higher cognitive performance than women. In addition, women were at low level of mobility and depended upon the daily living activities (p < 0.05). Both genders showed a significant negative correlation between mental status and functional independence or mobility level, while the correlation between functional independence and mobility level was significantly positive. The data showed that mental impairment decreases both functional status and mobility level of the institutionalized elderly people. Gender difference was found to be an important factor affecting the outcome variables of the study.

Activities of Daily Living↗

PubMed2005

Microfabricated refractive index gradient based detector for reversed-phase liquid chromatography with mobile phase gradient elution.

Typical refractive index (RI) detectors for liquid chromatography (LC) are not well suited to application with mobile phase gradient elution, due to the difficulty in correcting for the detected baseline shift during the gradient. We report a sensitive, highly reproducible, microfabricated refractive index gradient (micro-RIG) detector that performs well with mobile phase gradient elution LC. Since the micro-RIG signal remains on-scale throughout the mobile phase gradient, one can apply a baseline correction procedure. We demonstrate that by collecting two mobile phase gradient blanks and subtracting one of them from the other, a reproducible, flat baseline is achieved. Therefore, subtracting a blank from a separation provides a baseline corrected chromatogram with reasonably high signal-to-noise ratio for eluting analytes. The micro-RIG detector uses a collimated diode laser beam to optically probe a RIG formed perpendicular to the laminar flow direction within a microfabricated borosilicate glass chip. The chip-based design of the detector is suitable for either traditional bench-top or LC-on-a-chip technologies. We report reversed phase high performance liquid chromatography (RP-HPLC) separations of proteins and polymers, over mobile phase gradient conditions of 67% A:33% B to 3% A:97% B by volume, where A is 96% methanol:3.9% water:0.1% trifluoroacetic acid (TFA), and B is 3.9% methanol:96% water:0.1% TFA. The separations were performed on a Jupiter 5 mu C4 300 A 150 mm x 1.0 mm Phenomenex column at a flow rate of 20 microl/min. Viscosity changes during the mobile phase gradient separation are found to shift the on-chip merge position of the detected concentration gradient (i.e., RIG), in a reproducible fashion. However, this viscosity effect makes detection sensitivity vary throughout the mobile phase gradient, due to moving the optimized position of the probe beam in relation to the analyte concentration gradient being probed. None-the-less, consistent limits of detection (LODs) were achieved. The 3-sigma deflection angle LOD was 16 microrad for micro-RIG detection, corresponding to an injected concentration LOD of 7 ppm (mass/mass) for cytochrome c.

Chromatography, High Pressure Liquid↗

PubMed2005

Biosynthesis and mobilization of poly(3-hydroxybutyrate) [P(3HB)] by Spirulina platensis.

Three strains of Spirulina platensis isolated from different locations showed capability of synthesizing poly(3-hydroxybutyrate) [P(3HB)] under nitrogen-starved conditions with a maximum accumulation of up to 10 wt.% of the cell dry weight (CDW) under mixotrophic culture conditions. Intracellular degradation (mobilization) of P(3HB) granules by S. platensis was initiated by the restoration of nitrogen source. This mobilization process was affected by both illumination and culture pH. The mobilization of P(3HB) was better under illumination (80% degradation) than in dark conditions (40% degradation) over a period of 4 days. Alkaline conditions (pH 10-11) were optimal for both biosynthesis and mobilization of P(3HB) at which 90% of the accumulated P(3HB) was mobilized. Transmission electron microscopy (TEM) revealed that the mobilization of P(3HB) involved changes in granule quantity and morphology. The P(3HB) granules became irregular in shape and the boundary region was less defined. In contrast to bacteria, in S. platensis the intracellular mobilization of P(3HB) seems to be faster than the biosynthesis process. This is because in cyanobacteria chlorosis delays the P(3HB) accumulation process.

Adenosine Triphosphate↗

PubMed2004

Analysis of intrathoracic tumor mobility during whole breathing cycle by dynamic MRI.

PURPOSE: To assess diaphragm, lung region, and tumor mobility during the whole breathing cycle using dynamic MRI. A generalized safety margin concept for radiotherapy planning was calculated and compared with an individualized concept. METHODS AND MATERIALS: The breathing cycles of 20 patients with solitary lung tumors (15 Stage I non-small-cell lung carcinoma, 5 small solitary metastases) were examined with dynamic MRI (true Fast imaging with steady precision, three images per second). The deep inspiratory and expiratory positions of the diaphragm, upper, middle, and lower lung regions, and the tumor were measured in three dimensions. The mobility of tumor-bearing and corresponding tumor-free regions was compared. Tumor mobility in quiet respiration served as an MRI-based safety margin concept. RESULTS: The motion of the lung regions was significantly greater in the lower regions than in the upper regions (5 +/- 2 cm vs. 0.9 +/- 0.4 cm, p < 0.05). Tumor-bearing lung regions showed a significantly lower mobility than the corresponding noninvolved regions (p < 0.05). In quiet respiration, tumor mobility showed a high variability; a safety margin of 3.4 mm in the upper, 4.5 mm in the middle, and 7.2 mm in the lower region was calculated. CONCLUSION: Dynamic MRI is a simple, noninvasive method to evaluate intrathoracic tumor mobility for therapy planning. Because of the high variability of tumor mobility, an individual safety margin is recommended.

Adult↗

PubMed2005

From a postal questionnaire of older men, healthy lifestyle factors reduced the onset of and may have increased recovery from mobility limitation.

BACKGROUND AND OBJECTIVE: We have examined predictors of the onset of and recovery from mobility limitation and the association between lifestyle changes in later life and mobility status. STUDY DESIGN AND SETTING: From a cohort of 7,735 men recruited at ages 40-59 years (1978-1980), 5,075 men completed follow-up postal questionnaires in 1992 (Q92), then aged 52-73 years, and again in 1996 (Q96). Mobility limitation was defined as reported difficulty in any one or more of the following: getting outdoors, walking 400 yards, or climbing stairs. RESULTS: Lifestyle factors (smoking, obesity, physical inactivity, and heavy drinking) and manual worker social class were significantly and independently associated with onset of mobility limitation and with the exception of physical activity remained significant after further adjustment for chronic diseases. Smoking cessation and taking up physical activity in later life are associated with reduced onset of mobility limitation. Among men with mobility limitation at Q92 (n=645), light or moderate levels of physical activity were associated with significantly increased odds of recovery at Q96 (light activity, OR=2.43, 95% CI 1.48, 4.00; moderate activity, OR=2.57, 95% CI 1.31, 5.02). CONCLUSION: Maintaining and adopting a healthy lifestyle in later life reduces the onset of mobility limitation in old age. Maintaining physical activity may improve recovery.

Adult↗

PubMed2006

Manual forces applied during posterior-to-anterior spinal mobilization: a review of the evidence.

OBJECTIVE: The objective of this review was to evaluate the evidence for the consistency of force application by manual therapists when carrying out posterior-to-anterior (PA) mobilization techniques, including the factors that influence the application and measurement of mobilization forces. METHODS: Studies were identified by searching 6 electronic databases up to April 2005, screening the reference lists of retrieved articles, and contacting experts by e-mail. Relevant articles were defined as those that described the measurement of forces applied during spinal mobilization or discussed the reliability of measurement of manual forces. RESULTS: Twenty studies described the quantitative measurement of applied force during a PA mobilization technique, with most focusing on the lumbar spine. When defined by magnitude, frequency, amplitude, and displacement, PA mobilization forces are extremely variable among clinicians applying the same manual technique. Variability may be attributed to differences in techniques, measurement or reporting procedures, or variations between therapists or between patients. CONCLUSIONS: The inconsistency in manual force application during PA spinal mobilization in existing studies suggests that further studies are needed to improve the clinical standardization of manual force application. Future research on mobilization should include forces applied to the cervical and thoracic spines in addition to the lumbar spine while thoroughly describing force parameters and measurement methods to facilitate comparison between studies.

Evidence-Based Medicine↗

PubMed2007

Manual forces applied during cervical mobilization.

OBJECTIVE: Manual therapists routinely use passive accessory mobilization techniques to treat patients with mechanical neck disorders, but little is known about the manual forces applied. The aim of this study was to quantify the manual forces applied to the cervical spine during joint mobilization. METHODS: Ten physiotherapists performed posterior-to-anterior mobilizations to C2 and C7 (both centrally and unilaterally, 1 right and 1 left, grades I-IV) on a single asymptomatic male subject. Manual forces were measured in 3 planes using an instrumented treatment table. RESULTS: The instrumented table showed excellent reliability (intraclass correlation coefficient [2,1], 0.99; 95% confidence interval, 0.97-1.00) and accuracy (mean absolute error; vertical force, 1.1 N; SD, 1.5). There were considerable differences between therapists for mean peak force, force amplitude, and oscillation frequency for each technique and grade. Mean peak forces (grade I, 21.8 N; SD, 15.0; grade II, 34.9 N; SD, 20.9; grade III, 58.2 N; SD, 27.5; grade IV, 61.0 N; SD, 29.9) were considerably lower than previously reported lumbar mobilization forces. Intratherapist repeatability for all mobilization parameters was high. Force amplitude and oscillation frequency measures indicated that therapists generally adhered to the published definitions of the grades of mobilization when applying force, but when asked, provided quite different definitions of the grades. CONCLUSIONS: This study provides preliminary evidence that cervical mobilization forces vary considerably between therapists, but intratherapist repeatability is high.

Adult↗

PubMed2006

Mobile vs. fixed bearing unicondylar knee arthroplasty: A randomized study on short term clinical outcomes and knee kinematics.

The literature contains limited yet controversial information regarding whether a fixed or a mobile bearing implant should be used in unicompartmental knee arthroplasty (UKA). This randomized study was to further document the performance and comparison of the two designs. Fifty-six knees in 48 patients (mean age of 72 years) undergoing medial UKA were randomized into a fixed bearing (Miller/Galante) or a mobile bearing (Oxford) UKA. The 2 year clinical outcomes (clinical scores), radiographic findings, and weight bearing knee kinematics (assessed using RSA) were compared between the two groups. The mobile bearing knees displayed a larger and an incrementally increased tibial internal rotation (4.3 degrees, 7.6 degrees, 9.5 degrees vs. 3.0 degrees, 3.0 degrees, 4.2 degrees respectively at 30 degrees, 60 degrees, 90 degrees of knee flexion) compared to the fixed ones. The medial femoral condyle in the mobile bearing knees remained 2 mm from the initial position vs. a 4.2 mm anterior translation in the fixed bearing knees during knee flexion. The contact point in the mobile bearing implant moved 2 mm posteriorly vs. a 6 mm anterior movement in the other group. The mobile bearing knees had a lower incidence of radiolucency at the bone implant interface (8% vs. 37%, p < 0.05). The incidence of lateral compartment OA and progression of OA at patello-femoral joint were equal. No differences were found regarding Knee Society Scores, WOMAC, and SF-36 scores (p > 0.05). This study indicates that mobile bearing knees had a better kinematics, a lower incidence of radiolucency but not yet a better knee function at 2 years.

Aged↗

PubMed2006

Mobility of synaptic vesicles in different pools in resting and stimulated frog motor nerve terminals.

We used fluorescence recovery after photobleaching (FRAP) to measure the mobility of synaptic vesicles in frog motor nerve terminals. Vesicles belonging to the recycling pool or to the reserve pool were selectively labeled with FM1-43. In resting terminals, vesicles in the reserve pool were immobile, while vesicles in the recycling pool were mobile. Nerve stimulation increased the mobility of reserve pool vesicles. Treatment with latrunculin A, which destroyed actin filaments, had no significant effect on mobility, and reducing the temperature likewise had little effect, suggesting that recycling pool vesicles move by simple diffusion. Application of okadaic acid caused vesicle mobility in both pools to increase to the same level. We could model these and others' results quantitatively by taking into account the relative numbers of mobile and immobile vesicles in each pool, and vesicle packing density, which has a large effect on mobility.

Animals↗

PubMed2005

Conformation and mobility of the arabinan and galactan side-chains of pectin.

The function of the arabinan and galactan side-chains of pectin remains unknown. We describe 13C NMR experiments designed to yield spectra from the most mobile polymer components of hydrated cell walls isolated from a range of plant species. In pectin-rich cell walls, these corresponded to the pectic side-chains. The arabinan side-chains were in general more mobile than the galactans, but the long galactan side-chains of potato pectin showed high mobility. Due to motional line-narrowing effects these arabinan and galactan chains gave 13C NMR spectra of higher resolution than has previously been observed from 'solid' biopolymers. These spectra were similar to those reported for the arabinan and galactan polymers in the solution state, implying time-averaged conformations resembling those found in solution. The mobility of the highly esterified galacturonan in citrus cell walls overlapped with the lower end of the mobility range characteristic of the pectic side-chains. The cellulose-rich cell walls of flax phloem fibres gave spectra of low intensity corresponding to mobile type II arabinogalactans. Cell walls from oat coleoptiles appeared to contain no polymers as mobile as the pectic arabinans and galactans in primary cell walls of the other species examined. These properties of the pectic side-chains suggest a role in interacting with water.

Avena↗

PubMed2003

Establishing the reliability of Mobility Milestones as an outcome measure for stroke.

UNLABELLED: Baer GD, Smith MT, Rowe PJ, Masterton L. Establishing the reliability of mobility milestones as an outcome measure for stroke. Arch Phys Med Rehabil 2003;84:977-81. OBJECTIVE: To establish intrarater, interrater, and test-retest reliability of a standardized measure of mobility, "mobility milestones," incorporating sitting balance, standing balance, and walking ability. DESIGN: Repeated-measures reliability study by using video data of patients with stroke. SETTING: Physiotherapy and rehabilitation departments in Scotland. PARTICIPANTS: Forty physiotherapists recruited from within the Lothian region: 20 senior physiotherapists with at least 3 years of experience working with neurologic patients and 20 staff grade physiotherapists with less than 12 months of experience working with neurologic patients. INTERVENTION: Videotape comprising 40 clips (36 original clips, 4 repeated clips) of stroke patients of differing levels of ability attempting the mobility milestones was produced. After a short training session in the interpretation and application of the mobility milestones, each physiotherapist viewed the tape separately and scored whether the milestone had been achieved or not. This was repeated at a separate test session 2 weeks later. MAIN OUTCOME MEASURE: Score for each mobility milestone. RESULTS: Kappa statistics were used to determine interrater reliability and showed good (.61-.80) to very good (.81-1.0) reliability for 3 of 4 milestones. Intraclass correlation coefficients (ICCs) were used to determine intrarater reliability of the 4 repeated clips and showed 75% of all subjects had high (ICC(2,1)=.91-1.0) reliability. The ICC(2,1) for test-retest reliability showed a similar pattern, with 70% of subjects showing good (.81-.90) or high (.91-1.0) reliability. CONCLUSIONS: The mobility milestones showed favorable levels of reliability when used by experienced or novice physiotherapists. The milestones can be adopted as a simple clinical outcome measure for use with stroke. Further research is required to establish reliability levels when the measure is used by different rehabilitation professionals.

Activities of Daily Living↗

PubMed2004

Sit-and-reach test can predict mobility of patients recovering from acute stroke.

OBJECTIVES: To establish the test-retest reliability of the sit-and-reach test (SRT) and to determine the capacity of the SRT to predict mobility of patients recovering from acute stroke. DESIGN: Study 1 consisted of repeating the SRT to examine its reliability over trials (same day) and sessions (alternate days). Study 2 consisted of measuring performance in the SRT 7 to 10 days poststroke and measuring mobility at discharge for prospective analysis. SETTING: Medical and rehabilitation wards in hospital in Hong Kong. PARTICIPANTS: Thirty-six subjects with acute stroke (study 1, n=10; study 2, n=26). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Between 7 and 10 days of stroke onset, distance reached on the SRT was measured. Mobility at discharge was assessed using the transfer and locomotion scale of the FIM instrument (FIM mobility) and a timed walk test. RESULTS: The intertrial and intersession reliability of the SRT were rated good, with intraclass correlation coefficients of .98 and .79, respectively. Distance reached on the SRT correlated with the FIM mobility score on discharge (r=.572, P=.002) and the distance achieved on the timed walk test (r=.524, P=.006). Distance reached on the SRT accounted for 32.7% and 27.5% of the variance in the FIM mobility score at discharge and the distance achieved on the timed walk test, respectively. CONCLUSIONS: Performance in the SRT is reliable and can significantly predict the mobility of patients with acute stroke at discharge.

Aged↗

PubMed1999

Achievement of simple mobility milestones after stroke.

OBJECTIVES: To observe the mobility outcomes of an inpatient population of stroke patients grouped according to the Oxfordshire Community Stroke Project classification. STUDY DESIGN: "Mobility milestones," standardized measures of functional movement, were used to examine mobility recovery. PARTICIPANTS: Two hundred thirty-eight stroke patients admitted to the Western General Hospital, Edinburgh. MAIN OUTCOME MEASURES: Times taken to achieve four mobility milestones: 1-minute sitting balance, 10-second standing balance, a 10-step walk, and a 10-meter walk. RESULTS: For all subjects the median times to achieve the milestones were as follows: 1-minute sitting balance, day of stroke; 10-second standing balance, 3 days; 10-step walk, 6 days; and a 10-meter walk, 9 days. Subjects sustaining a partial anterior circulation infarct, lacunar infarct, or posterior circulation infarct achieved the mobility milestones most rapidly and generally had a shorter hospital stay. CONCLUSIONS: A hierarchical pattern of recovery of mobility reflecting variation between subgroups was observed. Predicted timescales for recovery of mobility are suggested.

Achievement↗

PubMed1997

Phosphatidic acid elicits calcium mobilization and actin polymerization through a tyrosine kinase-dependent process in human neutrophils: a mechanism for induction of chemotaxis.

Phospholipids mediate important effects as extracellular messengers in diverse biological systems. We investigated the effects of phosphatidic acid, a biologically active phospholipid potentially involved in the inflammatory process, on calcium mobilization and actin polymerization in human neutrophils and correlated these effects with induction of chemotactic migration. Intermediate-chain length phosphatidic acid (DiC10-PA) induced a biphasic increase in intracellular Ca2+ characterized by a rapid rise commencing immediately upon addition of stimulus followed by a secondary increase which, unlike the initial response, was eliminated by chelation of extracellular Ca2+. Neither of these responses were induced by C10-lysophosphatidic acid or diacylglycerol. The tyrosine kinase inhibitor herbimycin-A (5-10 microg/ml) completely blunted the initial but not the delayed response effected by DiC10-PA. Long-chain phosphatidic acid (DiC18:1) induced only an initial rapid increase in intracellular Ca2+ and this response was similarly markedly attenuated by herbimycin-A. Among several physiologically relevant phospholipids, only phosphatidic acid was able to induce Ca2+ mobilization; phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol -- used individually or in mixed liposomes -- were without effect. Phosphatidic acid conferred calcium-mobilizing activity upon inactive liposome preparations and phosphatidic acid-enriched cellular plasma membranes possessed similar calcium-mobilizing activity. Both DiC10-PA and DiC18:1-PA induced actin polymerization in neutrophils at rates which mirrored the influence of each agent on Ca2+ mobilization. Herbimycin-A blunted the initial increase in actin polymerization effected by phosphatidic acid but had no effect on the delayed, EGTA-sensitive phase. DiC10-PA and DiC18:1-PA also induced neutrophil migration along a concentration gradient. Phospholipids that failed to induce a calcium transient, including phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, and phosphatidylinositol, likewise failed to induce either actin polymerization or chemotactic migration. Unlike chemotaxis induced by zymosan-activated human serum, phosphatidate-induced chemotaxis was strongly inhibited by pretreatment of cells with herbimycin-A. Consistent with these observations, phosphatidic acid induced the tyrosine phosphorylation of several proteins as early as 10 s after stimulation. Phosphorylation of two distinct proteins with approximate molecular sizes of 72 and 82 kDa was inhibited by levels of herbimycin A used to effectively inhibit calcium mobilization, actin polymerization and chemotaxis. Thus, in neutrophilic leukocytes, extracellular phosphatidic acid induces a unique tyrosine kinase-based signalling pathway that results in calcium mobilization and actin polymerization. These processes may promote directed cellular migration as a consequence of the interaction of phosphatidic acid with neutrophil plasma membranes.

Actins↗

PubMed1999

T-cell stimulation through the T-cell receptor/CD3 complex regulates CD2 lateral mobility by a calcium/calmodulin-dependent mechanism.

T lymphocyte activation through the T cell receptor (TCR)/CD3 complex alters the avidity of the cell surface adhesion receptor CD2 for its ligand CD58. Based on the observations that activation-associated increases in intracellular [Ca2+] ([Ca2+]i) strengthen interactions between T cells and antigen-presenting cells, and that the lateral mobility of cell surface adhesion receptors is an important regulator of cellular adhesion strength, we postulated that [Ca2+]i controls CD2 lateral mobility at the T cell surface. Human Jurkat T leukemia cells were stimulated by antibody-mediated cross-linking of the TCR/CD3 complex. CD2 was labeled with a fluorescently conjugated monoclonal antibody. Quantitative fluorescence microscopy techniques were used to measure [Ca2+]i and CD2 lateral mobility. Cross-linking of the TCR/CD3 complex caused an immediate increase in [Ca2+]i and, 10-20 min later, a decrease in the fractional mobility of CD2 from the control value of 68 +/- 1% to 45 +/- 2% (mean +/- SEM). One to two hours after cell stimulation the fractional mobility spontaneously returned to the control level. Under these and other treatment conditions, the fraction of cells with significantly elevated [Ca2+]i was highly correlated with the fraction of cells manifesting significantly reduced CD2 mobility. Pretreatment of cells with a calmodulin inhibitor or a calmodulin-dependent kinase inhibitor prevented Ca2+-mediated CD2 immobilization, and pretreatment of cells with a calcineurin phosphatase inhibitor prevented the spontaneous reversal of CD2 immobilization. These data suggest that T cell activation through the TCR/CD3 complex controls CD2 lateral mobility by a Ca2+/calmodulin-dependent mechanism, and that this mechanism may involve regulated phosphorylation and dephosphorylation of CD2 or a closely associated protein.

Biophysical Phenomena↗

PubMed2000

Influence of mobile phase composition and cross-linking density on the enantiomeric recognition properties of molecularly imprinted polymers.

A series of experiments were conducted to investigate elements which affect the enantiomeric recognition properties of molecularly imprinted polymers (MIPs) in the HPLC mode. Our results show that the recognition properties of MIPs are greatly influenced by the mobile phase used. For a polymer prepared in acetonitrile, a good enantiomeric separation was observed when acetonitrile-based mobile phase was used, when the mobile phase was changed to chloroform-based, no enantiomeric recognition was observed although the sample molecule was retarded. This indicates that the specific co-operative binding interactions between the functional groups at the imprinted polymer's recognition sites and the sample molecule were considerably disrupted and only non-specific interactions remained. When the mobile phase was changed back to acetonitrile-based, the recognition was regained. In contrast, for polymers prepared in chloroform, chloroform-based mobile phase gave much better separation than acetonitrile-based mobile phase. When other solvents were tested, significant solvent effects were generally observed. Based on these observations, the recognition properties of the methacrylic acid (MAA)-co-ethylene glycol dimethacrylate (EGDMA) polymers were reinvestigated, and the results show that by simply using an optimised mobile phase system, significantly improved recognition over previously reported results was observed. For a polymer made against Cbz-L-Trp, 100 microg of Cbz-D,L-Trp was separated with a separation factor (alpha) of 4.23 and a resolution (Rs) of 3.87, whereas in the previous report, 10 microg of Cbz-D,L-Trp was only separated with alpha = 1.67 and Rs = 0.1. It is generally realised that the imprinted polymer's recognition property is also very much influenced by the nature of the polymer network. It was shown that the recognition decreased with a decrease in the apparent degree of cross-linking (molar percentage of cross-linker in the polymerisation mixture). Nonetheless, our results show that in our optimised assay system a significant separation could still be obtained on a polymer which was only 22% cross-linked. We consider this to be of importance, since it may suggest a way of imprinting larger molecules because of the possibly improved mass transfer in low cross-linking density polymers. It was reported that when trifunctional cross-linkers [for example: trimethylolpropane trimethacrylate (TRIM)] were used as the cross-linker instead of EGDMA, considerably improved enantiomeric separation and resolving capability were observed. Our results show that the improved performance of the MAA-co-EGDMA MIPs is actually comparable to the performance of the MIPs prepared with those trifunctional cross-linkers. The combination of a hydrogen bonding functional monomer (acrylamide) with TRIM also did not give improved recognition. The results suggest that although the three-dimensional network of these two kinds of polymer may be quite different, the observed recognition improvements were probably largely due to solvent effect.

Chromatography, High Pressure Liquid↗