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91.
Adam Zipp Irwin D. Kuntz Thomas L. James 《Archives of biochemistry and biophysics》1977,178(2):435-441
The dependence of the water proton magnetic resonance spin-lattice relaxation rate (T1??1) in the rotating frame on the strength of the spin-locking (H1) field has been investigated for packed oxy and deoxy normal and sickle erythrocytes at temperatures from 9 to 40 °C. The T1??1 of oxy or deoxy normal erythrocytes shows no dependence on H1 up to ~7 G at any temperature studied. On the other hand, T1??1 decreases from about 40 s?1 to 15 s?1 (H1 from 0 to ~7 G) for deoxygenated packed sickle cells at 40 °C. The magnitude of this variation of T1??1 with H1 decreases with decreasing temperature. Oxy packed sickle cells also show a dependence of T1??1 on H1 but the magnitude is <10% of that of the deoxygenated samples. These results suggest that water proton T1??1 measurements are a sensitive probe of hemoglobin S polymerization and provide a novel technique for the study of slow water motions in these systems. The T1??1 results are compared with low frequency T1?1 results of other investigators on hemoglobin S solutions. Analysis of the data suggests that water proton motions with correlation times of the order of 10?5 s are present in the deoxygenated sickle cell samples at temperatures above 10 °C. 相似文献
92.
93.
Summary We have recently shown that stimulation of electrogenic HCO
3
–
secretion is accompanied by a simultaneous increase in short-circuit current (I
sc, equivalent to HCO
3
–
secretion rate under these conditions), apical membrane capacitance (C
a
, proportional to membrane area), and apical membrane conductance (G
a
, proportional to membrane ionic permeability). The current experiments were undertaken to explore the ionic basis for the increase inG
a
and the possibility that the rate of electrogenic HCO
3
–
secretion is regulated by changes inG
a
. Membrane electrical parameters were measured using impedance-analysis techniques before and after stimulation of electrogenic HCO
3
–
secretion with cAMP in three solutions which contained different chloride concentrations. In another series of experiments, the effects of an anion channel blocker, anthracene-9-carboxylic acid (9-AA), were measured after stimulation of electrogenic HCO
3
–
secretion with cAMP. The major conclusions are: (i) a measurable apical Cl– conductance exists in control hemibladders; (ii) the transport-associated increase inG
a
includes a Cl–-conductive component; (iii)G
a
also appears to reflect a HCO
3
–
conductance; (iv) the relative magnitudes of the apical membrane conductances to Cl– and HCO
3
–
are similar; (v) 9-AA reducesG
a
andI
sc appear cAMP-stimulated hemibladders; and (vi) alterations inI
sc appear to be mediated by changes inG
a
. 相似文献
94.
R D Adam 《Microbiology and molecular biology reviews》1991,55(4):706-732
Gardia spp. are flagellated protozoans that parasitize the small intestines of mammals, birds, reptiles, and amphibians. The infectious cysts begin excysting in the acidic environment of the stomach and become trophozoites (the vegetative form). The trophozoites attach to the intestinal mucosa through the suction generated by a ventral disk and cause diarrhea and malabsorption by mechanisms that are not well understood. Giardia spp. have a number of unique features, including a predominantly anaerobic metabolism, complete dependence on salvage of exogenous nucleotides, a limited ability to synthesize and degrade carbohydrates and lipids, and two nuclei that are equal by all criteria that have been tested. The small size and unique sequence of G. lamblia rRNA molecules have led to the proposal that Giardia is the most primitive eukaryotic organism. Three Giardia spp. have been identified by light lamblia, G. muris, and G. agilis, but electron microscopy has allowed further species to be described within the G. lamblia group, some of which have been substantiated by differences in the rDNA. Animal models and human infections have led to the conclusion that intestinal infection is controlled primarily through the humoral immune system (T-cell dependent in the mouse model). A major immunogenic cysteine-rich surface antigen is able to vary in vitro and in vivo in the course of an infection and may provide a means of evading the host immune response or perhaps a means of adapting to different intestinal environments. 相似文献
95.
96.
A L Back W W Kwok M Adam S J Collins D D Hickstein 《Biochemical and biophysical research communications》1990,171(2):787-795
Children with leukocyte adherence deficiency (LAD) exhibit heterogeneous defects in the leukocyte integrin CD18 subunit that prevent surface expression of functional CD11/CD18 leukocyte integrin adherence complexes. We used a retroviral vector, designated LCD18SN, to transfer the CD18 cDNA into K562 human myeloid leukemia cells and into EBV B-cells from a child with LAD. Transfer of the LCD18SN retroviral construct, which expresses the CD18 cDNA from the Moloney Murine leukemia virus (MoMLV) long terminal repeat (LTR), into K562 cells resulted in relatively high levels of CD18 mRNA and intracellular protein. Retroviral-mediated gene transfer of CD18 into LAD EBV B-cells resulted in low, but readily measurable, levels of surface expression of the CD11a/CD18 complex in these previously deficient lymphocytes. The reconstitution of surface expression of the CD11a/CD18 complex by gene transfer of the CD18 cDNA into LAD EBV B-cells indicates that this syndrome represents a candidate disorder for gene therapy. 相似文献
97.
Genes Responsible for Size Reduction of Marine Vibrios during Starvation Are Located on the Chromosome 总被引:2,自引:1,他引:1
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In a survey of 21 marine Vibrio spp., all responded to nutrient deprivation by undergoing a reduction in size (dwarfing). However, only 43% of these strains possessed one or more plasmids, suggesting that the genes responsible for dwarfing were located on the chromosome rather than on the plasmids. This conclusion was confirmed by the observation that fragmentation and subsequent size reduction occurred in three strains from which the plasmids had been removed by curing. The cured strains lost certain characteristics, such as resistance to some heavy metals and antibiotics, that were restored when the plasmids were reintroduced by either transformation or electroporation. 相似文献
98.
The synthetic immunomodulator muramyldipeptide (MDP) can stimulate B cells. MDP, when used alone, was apparently unable to induce the differentiation or proliferation of resting B cells. In contrast, MDP appeared to synergize with a single recombinant interleukin (IL) to stimulate either their differentiation or proliferation. We used single interleukins to avoid synergistic and antagonistic effects inherent in the use of several factors. IL-2 was found to be sufficient to restore the specific immune response of resting B cells to sheep erythrocytes; MDP greatly increased the number of plaque-forming cells of such IL-2-stimulated B cells. In contrast, IL-4 and interferon-gamma (IFN-gamma), either alone or in the presence of MDP, had no effect in this differentiation assay. MDP was also able to stimulate polyclonally activated B cells. IL-4 increased the proliferation of anti-IgM-stimulated B cells, leading to enlargement and driving more cells into the cell cycle; these effects were further enhanced by MDP, more cells being induced to proliferate, to enlarge, and to progress into the cycle with a higher frequency of cells in the G1B, S, and G2/M compartments. Intracellular free calcium levels were not increased by IL-4 and/or MDP, and the two compounds did not modify the anti-IgM-induced calcium mobilization. Therefore, MDP appears to amplify cytokine effects in B cell activation, by a mechanism which does not appear to involve free calcium mobilization. 相似文献
99.
Subpopulations of different proliferative status are determined during cell-density dependent proliferation of 3T3 cells. From these data the probability of conversion of proliferative to quiescent cells is derived and found to correlate well with published data on binding of growth-inhibiting factors secreted from growth-inhibited cells.Based on material presented at the Symposium Intercellular Communication Stuttgart, September 16–17, 1982 相似文献
100.
Cysteamine is under investigation as an aid in radiation therapy and as a treatment for the inherited disorder cystinosis. An assay is presented for its measurement in biological fluids. The specific reaction of thiosulfonates with sulfhydryl compounds is employed to form a radiolabeled derivative of cysteamine which is then isolated by high-voltage electrophoresis on paper. Cysteamine can be measured in aqueous solutions, plasma, and urine with this method. 相似文献