Biomedical subjects

Z Xia

Publications and source records attributed to Z Xia.

153 records · Page 9Linked to original sources

PubMed1992

Stimulation of the type III olfactory adenylyl cyclase by calcium and calmodulin.

Characterization of adenylyl cyclases has been facilitated by the isolation of cDNA clones for distinct adenylyl cyclases including the type I and type III enzymes. Expression of type I adenylyl cyclase activity in animal cells has established that this enzyme is stimulated by calmodulin and Ca2+. Type III adenylyl cyclase is enriched in olfactory neurons and is regulated by stimulatory G proteins. The sensitivity of the type III adenylyl cyclase to Ca2+ and calmodulin has not been reported. In this study, type III adenylyl cyclase was expressed in human kidney 293 cells to determine if the enzyme is stimulated by Ca2+ and calmodulin. The type III enzyme was not stimulated by Ca2+ and calmodulin in the absence of other effectors. It was, however, stimulated by Ca2+ through calmodulin when the enzyme was concomitantly activated by either GppNHp or forskolin. The concentrations of free Ca2+ for half-maximal stimulation of type I and type III adenylyl cyclases were 0.05 and 5.0 microM Ca2+, respectively. These data suggest that the type III adenylyl cyclase is stimulated by Ca2+ when the enzyme is activated by G-protein-coupled receptors and that increases in free Ca2+ accompanying receptor activation may amplify the primary cyclic AMP signal.

Adenylyl Cyclases↗

PubMed1989

Microrheological aspects of adhesion of Escherichia coli on glass.

The adhesion of both live and fixed bacteria (Escherichia coli) on glass has been studied under well-defined hydrodynamic conditions, created in an impinging jet apparatus. With this technique one can accurately measure the initial deposition rate jo on the surface, the average lifetime of a bacterium on the surface, tau esc, and the surface area blocked per deposited bacterium, normalized by its projected area, gamma. The experimental results are compared to theoretical results for equivalent spheres. It is found that near the stagnation point the deposition rate jo is mainly controlled by convective diffusive transport which, for rod-shaped Eschericia coli, with an axis ratio of about 2, is found to be equal to that for spheres. No differences in jo and tau esc were found between live and fixed bacteria at low flow rates. At high flow rates fixed bacteria adhered to the surface at a slower rate. In both systems jo was found to decrease suddenly at a distance of about 150 microns from the stagnation point, in contrast to systems of spherical particles for which jo is uniform over the surface. Most likely this is due to the rotation of the rod-shaped particles, which vary their distance to the surface periodically with time. The main difference between live and fixed bacteria, besides different deposition rates in strong flows, is that gamma is about 30% larger for fixed bacteria than for live ones, resulting in a much lower final coverage for fixed bacteria. These results imply a larger repulsion between fixed bacteria than between living ones. From detachment experiments we can conclude that not all bacteria stick to the surface with the same bond strength. The variation in the bond strength is due to the aging of the bonds between the bacteria and the surface. The average bond strength corresponds to an energy of about 13-15 kT.

Bacterial Adhesion↗

PubMed1986

Preliminary X-ray crystallographic study of methanol dehydrogenase from Methylophilus methylotrophus.

Single crystals of methanol dehydrogenase from Methylophilus methylotrophus have been prepared by the macroseeding method. The crystals belong to the monoclinic space group C2, and have unit cell parameters a = 125.62 A, b = 63.83 A, c = 83.99 A, and beta = 93.24 degrees. There is one 62,000 Mr monomer in the asymmetric unit. The crystals diffract to beyond 2.0 A resolution.

Alcohol Oxidoreductases↗

PubMedDate not supplied

Biorheological features of some soft tissues under a surgical tissue expansion procedure.

The aim of this study was to investigate the effects of a surgical tissue expansion procedure on the biomechanical features of the expanded soft tissues. In this procedure a silicone balloon "expander" is surgically inserted into a tissue and inflated. The tissue mass increases under the stretch of the expander. The increased tissue can then be used as an autologous source for the surgical reconstruction of organs. In this article, dog saphenous neurovascular bundle was used. Expanded saphenous nerves, arteries and veins were harvested and their biomechanical features and ultrastructural, histological changes were studied. The stress relaxation features, the continuous spectrum of relaxation time, and the stress-strain relationship of expanded and control specimens were measured. Results show that within two or three weeks after placement of the expanders, the biomechanical properties of expanded saphenous nerves, arteries and veins began to deviate from those of their controls, and the differences between them were proportional to the volume of inflation; but when the expanding period was 15 weeks or longer, the properties of expanded specimens and their controls became close again. Histological study showed that the content of collagenous fibers in blood vessel walls decreased after expansion. The content of elastic fibers in blood vessel walls first increased, then returned to normal, and finally decreased. Ultrastructural studies showed that when elongated by 25-40%, the expanded nerves had well preserved axons and showed fewer smooth myelin sheaths only in the middle and distal part of the expansion.

Animals↗

PubMedDate not supplied

Tricyclic antidepressants induce apoptosis in human T lymphocytes.

Apoptosis is a form of programmed cell death that is involved in cell turnover. In the present study we show that the tricyclic antidepressants (TCAS) imipramine, clomipramine and citalopram induce apoptosis in human peripheral lymphocytes. Lymphocytes were incubated with these three drugs for up to 48 h. Apoptosis was characterized by typical nucleosomal DNA fragmentation on agarose gel, as well as quantitated using 4'-6-diamidino-2-phenylindole (DAPI) staining and 3'-OH end-labeling of fragmented DNA at the single cell level. Apoptosis induced by TCAs was shown to be dose-dependent and could be detected after a 24 h incubation. The optimal concentrations of the three TCAs found to induce apoptosis were 50 microM imipramine, 20 microM clomipramine and 180 microM citalopram. Furthermore, immunofluorescence and three-color flow cytometry were used to identify the phenotype of apoptotic cells. TCA-induced apoptosis was shown to involve exclusively T-lymphocytes. Cytotoxic T-lymphocytes were more prone to undergo apoptosis than were T-helper cells. In conclusion, the present investigation clearly demonstrates that TCAs exert cell biological effects upon human T-lymphocytes. Further studies are required to determine the possible clinical relevance of these findings.

Adult↗

PubMedDate not supplied

Stimulation of fibroblast growth in vitro by intermittent radiant warming.

A number of clinical studies have suggested that radiant heat improves the healing of selected acute and chronic wounds. The purpose of this study was to investigate in vitro the effect of intermittent radiant heating on the growth of human skin fibroblasts using a radiant heat-producing dressing with a designated temperature of 38 degrees C. In initial experiments cells were seeded in six well-plates, maintained in culture at 33-34 degrees C, and warmed daily for three cycles of 1 hour with 1.5 hour intervals. Changes in cell growth and metabolism were determined in sets of triplicate wells by cell counts and a colorimetric assay before and after one week's treatment. After eight days the number of cells in the radiant heat-treated group was 30% higher and the metabolic activity 47%- 90% higher than in the control group. In quiescent fibroblasts which had been maintained for four weeks in low-serum medium, the warming regime completely prevented the decrease in cell number observed in control cells. Our findings suggest that the stimulation of cell proliferation induced by intermittent heating in vitro may indicate a possible mechanism contributing to in vivo effects.

Adolescent↗

PubMedDate not supplied

Fatal occupational injuries in the construction industry of a new development area in east China, 1991 to 1997.

Two hundred thirty-five work-related deaths occurred in the construction industry in a new economic development area in eastern China between 1991 and 1997. These fatalities represented 55% of all occupational deaths. The average annual mortality rate was 51.5 per 100,000 construction workers. Falls were the leading cause of death (46.4%). Falls, collisions, struck by/against something, electrocutions, and excavation cave-ins were the main fatality antecedents, accounting for nearly 93.6% of all fatalities. The most common antecedents for incidents with multiple fatalities were falls, crane-related events, poisoning, and fire. These categories of antecedents were similar to those encountered in the construction industry in the United States. These data suggest that organizations need to focus on these event types when planning their prevention activities. Moreover, improved surveillance systems including computerized databases with narrative descriptions of injury events, antecedent factors, and person-time at-risk data are needed to target interventions more precisely.

Accidents, Occupational↗

PubMedDate not supplied

NMR relaxation studies on hepatic intracellular and extracellular sodium in rats with burn injury.

In vivo longitudinal (T1) and transverse (T2) relaxation times of hepatic intracellular and extracellular sodium were studied in rats with sham burn or burn injury with 23Na NMR spectroscopy and shift reagent. Burn injury decreases hepatic extracellular sodium content by 17% compared with sham burn, whereas it increases the percent of the fast T2 component of extracellular sodium, suggesting an increase in the fraction of bound Na+/- sites in the extracellular space. It is interesting that the relaxation characteristics of intracellular sodium remained unchanged despite a 57% increase in intracellular sodium content, suggesting the increase in intracellular free sodium is matched by either a proportional increase in intracellular bound sodium or an uncovering of ordered domain sites that can preferentially orient rapidly exchanging sodium ions. This study also demonstrated that spin lattice (T1) relaxation rates or the percent contribution of the fast/slow T2 components of the combined intracellular/extracellular 23Na signal (before the infusion of shift reagent) may also be sensitive to changes in intracellular sodium levels during pathologic changes.

Animals↗

PubMedDate not supplied

Barriers to immunization in a relatively affluent community.

BACKGROUND: Although Healthy People 2000 calls for the complete immunization of at least 90% of children by age 20 months, few communities can claim such success. We wanted to determine the parent-reported barriers associated with underimmunization of infants in a relatively affluent midwestern population. METHODS: We undertook a case-control study of a population-based sample of parents and guardians of children who were either fully immunized or underimmunized at 20 months of age in Olmsted County, Minn. RESULTS: In this study, 596 of 1,216 parents (46%) of both immunized and underimmunized children participated. Of these participants, 281 (47%) reported barriers to immunizations, but only 15 (3%) reported major barriers. Whereas the most commonly reported barriers were barriers of inconvenience (waiting too long, inconvenient office hours), only delays caused by a sick child, fear of reactions, trouble remembering an appointment, not knowing when the next shot was due, and transportation problems were significantly associated with underimmunization when controlling for demographic factors. Fear of reactions, sick child delays, and not knowing when the next shot was due had the highest attributable risk for underimmunization. Taken together, parent-reported barriers and demographic factors explained less than 30% of the underimmunization status of children. Parents' most common recommendations for improving immunization status were the use of a recall or reminder system and a single unified schedule for immunizations. CONCLUSIONS: In this relatively affluent community, barriers to immunization were commonly reported but few (fear of reactions, sick child delays, and not knowing when the next shot was due) were associated with underimmunization. The types of barriers reported were similar to those reported in other communities, but unlike many populations studied, cost was not reported as an important barrier.

Case-Control Studies↗