Hemoglobin-water interactions in normal and sickle erythrocytes by proton magnetic resonance T1ϱ measurements

The dependence of the water proton magnetic resonance spin-lattice relaxation rate (T_1?^?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 T_1?^?1 of oxy or deoxy normal erythrocytes shows no dependence on H₁ up to ~7 G at any temperature studied. On the other hand, T_1?^?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 T_1?^?1 with H₁ decreases with decreasing temperature. Oxy packed sickle cells also show a dependence of T_1?^?1 on H₁ but the magnitude is <10% of that of the deoxygenated samples. These results suggest that water proton T_1?^?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 T_1?^?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.     

Electrogenic bicarbonate secretion in the turtle bladder: Apical membrane conductance characteristics

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 .     

Vasopressin alters the mechanism of apical Cl− entry from Na+:Cl− to Na+:K+:2Cl− cotransport in mouse medullary thick ascending limb

Summary Experiments were performed usingin vitro perfused medullary thick ascending limbs of Henle (MTAL) and in suspensions of MTAL tubules isolated from mouse kidney to evaluate the effects of arginine vasopressin (AVP) on the K⁺ dependence of the apical, furosemide-sensitive Na⁺:Cl^– cotransporter and on transport-related oxygen consumption (QO₂). In isolated perfused MTAL segments, the rate of cell swelling induced by removing K⁺ from, and adding onemm ouabain to, the basolateral solution [ouabain(zero-K⁺)] provided an index to apical cotransporter activity and was used to evaluated the ionic requirements of the apical cotransporter in the presence and absence of AVP. In the absence of AVP cotransporter activity required Na⁺ and Cl^–, but not K⁺, while in the presence of AVP the apical cotransporter required all three ions.⁸⁶Rb⁺ uptake into MTAL tubules in suspension was significant only after exposure of tubules to AVP. Moreover,²²Na⁺ uptake was unaffected by extracellular K⁺ in the absence of AVP while after AVP exposure²²Na⁺ uptake was strictly K⁺-dependent. The AVP-induced coupling of K⁺ to the Na⁺:Cl^– cotransporter resulted in a doubling in the rate of NaCl absorption without a parallel increase in the rate of cellular²²Na⁺ uptake or transport-related oxygen consumption. These results indicate that arginine vasopressin alters the mode of a loop diuretic-sensitive transporter from Na⁺:Cl^– cotransport to Na⁺:K⁺:2Cl^– cotransport in the mouse MTAL with the latter providing a distinct metabolic advantage for sodium transport. A model for AVP action on NaCl absorption by the MTAL is presented and the physiological significance of the coupling of K⁺ to the apical Na⁺:Cl^– cotransporter in the MTAL and of the enhanced metabolic efficiency are discussed.     

The biology of Giardia spp.

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.     

冬小麦春化过程中低温诱导的与花芽分化相关的mRNA和蛋白质的合成

应用SDS电泳及高分辨双向电泳技术,分析了冬小麦经春化、脱春化及超期春化处理后茎类蛋白质组分的变化。发现52.5,38kD和16.2kD蛋白质与冬小麦开花诱导密切相关。mRNA体外翻译结果表明,春化作用中低温诱导与开花紧密相关的mRNA的出现有一定的顺序性。因此推测:春化诱导开花是低温导致某些特定基因表达的结果,而表达的调节主要发生在转录水平上。     

Retroviral-mediated gene transfer of the leukocyte integrin CD18 subunit

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.     

Genes Responsible for Size Reduction of Marine Vibrios during Starvation Are Located on the Chromosome

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.     

Muramyl dipeptide (MDP) synergizes with interleukin 2 and interleukin 4 to stimulate, respectively, the differentiation and proliferation of B cells

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.