Intracellular ADP activates K+ channels that are inhibited by ATP in an insulin-secreting cell line

The effect of ADP on ATP-sensitive K+ channels in the insulin-secreting RINm5F cell line has been investigated with the help of single-channel current recording from saponin-permeabilized cells. ADP (100-500 microM) markedly activates K+ channels when added to the bath solution in contact with the membrane inside. ADP-beta-S cannot mimick this effect. During sustained ATP (500 microM)-evoked inhibition of K+ channel opening, 500 microM ADP markedly and reversibly activates the channels. Conversely ATP markedly reduces the opening probability of ADP-activated channels. It is suggested that the physiological control of K+ channel opening in the insulin-secreting cells is mediated by changes in ATP/ADP ratio rather than being solely determined by the ATP concentration.     

Partial purification and characterization of a polymannuronic acid depolymerase produced by a mucoid strain of Pseudomonas aeruginosa isolated from a patient with cystic fibrosis.

An exopolysaccharide depolymerase was isolated from a mucoid strain of Pseudomonas aeruginosa of cystic fibrosis origin. Purified preparations of the depolymerase showed maximum activity against the unacetylated polymannuronic acid exopolysaccharide from the same strain and little activity against commercially prepared alginic acid. The evidence suggests that the enzyme is either periplasmic in location or associated with the outer cell membrane and is released extracellularly, in the absence of cell lysis, after a reduction of the culture magnesium (Mg2+) concentration below 3.0 mM. The depolymerase is also released after the addition of sublethal concentrations of EDTA to cultures containing 3.0 mM Mg2+. A survey of additional mucoid P. aeruginosa isolates recovered from patients with cystic fibrosis showed that nearly 60% demonstrated similar depolymerase activity while none of the nonmucoid revertants of the parent strains produced detectable depolymerase activity.     

ATP-sensitive inward rectifier and voltage- and calcium-activated K+ channels in cultured pancreatic islet cells

Summary K⁺ channels in cultured rat pancreatic islet cells have been studied using patch-clamp single-channel recording techniques in cell-attached and excised inside-out and outside-out membrane patches. Three different K⁺-selective channels have been found. Two inward rectifier K⁺ channels with slope conductances of about 4 and 17 pS recorded under quasi-physiological cation gradients (Na⁺ outside, K⁺ inside) and maximal conductances recorded in symmetrical K⁺-rich solutions of about 30 and 75 pS, respectively. A voltage- and calcium-activated K^– channel was recorded with a slope conductance of about 90 pS under the same conditions and a maximal conductance recorded in symmetrical K⁺-rich solutions of about 250 pS. Single-channel current recording in the cell-attached conformation revealed a continuous low level of activity in an apparently small number of both the inward rectifier K⁺ channels. But when membrane patches were excised from the intact cell a much larger number of inward rectifier K⁺ channels became transiently activated before showing an irreversible decline. In excised patches opening and closing of both the inward rectifier K⁺ channels were unaffected by voltage, internal Ca²⁺ or externally applied tetraethyl-ammonium (TEA) but the probability of opening of both inward rectifier K⁺ channels was reduced by internally applied 1–5mm adenosine-5-triphosphate (ATP). The large K⁺ channel was not operational in cell-attached membrane patches, but in excised patches it could be activated at negative membrane potentials by 10^–7 to 10^–6 m internal Ca²⁺ and blocked by 5–10mm external TEA.     

Functional role of human IgG subclasses in eosinophil-mediated killing of schistosomula of Schistosoma mansoni

Although IgG antibodies and eosinophils have been shown to kill schistosomula of Schistosoma mansoni in vitro, very little data exist that describe the role of each IgG antibody isotype in this event. This study was designed to test the role of each IgG subclass in the eosinophil-dependent killing reaction. IgG antibodies purified by protein G or protein A affinity chromatography demonstrated a killing effect only in the presence of eosinophils activated in vivo or normal eosinophils activated in vitro by eosinophil activating factor. Purification of each IgG isotype allowed confirmation of these results and demonstrated that the killing effect was associated with IgG1 and IgG3 antibodies. IgG2 antibodies expressed a dual function: 1) an effector function with activated eosinophils and 2) a blocking function with normal eosinophils. IgG4 antibodies, whatever the source of eosinophils, blocked the killing mediated by IgG effector antibodies. These findings are discussed in relation to immunity and susceptibility to reinfection in human schistosomiasis.     

Extracellular ATP causes Ca2(+)-dependent and -independent insulin secretion in RINm5F cells. Phospholipase C mediates Ca2+ mobilization but not Ca2+ influx and membrane depolarization

The mechanism by which extracellular ATP stimulates insulin secretion was investigated in RINm5F cells. ATP depolarized the cells as demonstrated both by using the patch-clamp technique and a fluorescent probe. The depolarization is due to closure of ATP-sensitive K+ channels as shown directly in outside-out membrane patches. ATP also raised cytosolic Ca2+ [( Ca2+]i). At the single cell level the latency of the [Ca2+]i response was inversely related to ATP concentration. The [Ca2+]i rise is due both to inositol trisphosphate mediated Ca2+ mobilization and to Ca2+ influx. The former component, as well as inositol trisphosphate generation, were inhibited by phorbol myristate acetate which uncouples agonist receptors from phospholipase C. This manoeuvre did not block Ca2+ influx or membrane depolarization. Diazoxide, which opens ATP-sensitive K+ channels, attenuated membrane depolarization and part of the Ca2+ influx stimulated by ATP. However, the main Ca2+ influx component was unaffected by L-type channel blockers, suggesting the activation of other Ca2+ conductance pathways. ATP increased the rate of insulin secretion by more than 12-fold but the effect was transient. Prolonged exposure to EGTA dissociated the [Ca2+]i rise from ATP-induced insulin secretion, since the former was abolished and the latter only decreased by about 60%. In contrast, vasopressin-evoked insulin secretion was more sensitive to Ca2+ removal than the accompanying [Ca2+]i rise. Inhibition of phospholipase C stimulation by phorbol myristate acetate abrogated vasopressin but only reduced ATP-induced insulin secretion by 34%. These results suggest that ATP stimulates insulin release by both phospholipase C dependent and distinct mechanisms. The Ca2+)-independent component of insulin secretion points to a direct triggering of exocytosis by ATP.     

Genome-Wide Association Studies in an Isolated Founder Population from the Pacific Island of Kosrae

It has been argued that the limited genetic diversity and reduced allelic heterogeneity observed in isolated founder populations facilitates discovery of loci contributing to both Mendelian and complex disease. A strong founder effect, severe isolation, and substantial inbreeding have dramatically reduced genetic diversity in natives from the island of Kosrae, Federated States of Micronesia, who exhibit a high prevalence of obesity and other metabolic disorders. We hypothesized that genetic drift and possibly natural selection on Kosrae might have increased the frequency of previously rare genetic variants with relatively large effects, making these alleles readily detectable in genome-wide association analysis. However, mapping in large, inbred cohorts introduces analytic challenges, as extensive relatedness between subjects violates the assumptions of independence upon which traditional association test statistics are based. We performed genome-wide association analysis for 15 quantitative traits in 2,906 members of the Kosrae population, using novel approaches to manage the extreme relatedness in the sample. As positive controls, we observe association to known loci for plasma cholesterol, triglycerides, and C-reactive protein and to a compelling candidate loci for thyroid stimulating hormone and fasting plasma glucose. We show that our study is well powered to detect common alleles explaining ≥5% phenotypic variance. However, no such large effects were observed with genome-wide significance, arguing that even in such a severely inbred population, common alleles typically have modest effects. Finally, we show that a majority of common variants discovered in Caucasians have indistinguishable effect sizes on Kosrae, despite the major differences in population genetics and environment.     

Comparative ultrastructure of a mucoid strain of Pseudomonas aeruginosa isolated from cystic fibrosis patient and its spontaneous non-mucoid mutant

The ultrastructure of a mucoid strain of Pseudomonas aeruginosa of cystic fibrosis origin and its spontaneous non-mucoid variant was compared by transmission electron microscopy. Negatively-stained preparations of the mucoid strain obtained from plate cultures demonstrated dense, fibrous material projecting from the cell. No such material was observed in thin-sections or in negatively-strained preparations from liquid cultures. Thin-sections of ethanol-precipitated extracellular material from liquid cultures of the mucoid-strain revealed a cottony mesh of thin electron dense fibres. The non-mucoid strain did not produce such material. When prefixed with glutaraldehyde/malachite green mixture, cells of both strains demonstrated electron dense intracellular and extracellular malachite green-stainable structures. The internal complexes were frequently associated with the nucleoid or cell membrane and were replaced by electron transparent areas in cells prefixed with glutaraldehyde alone. Aeruginocins of the R-type were observed in mitomycin C induced cultures of both strains. Bacteriophages with 'claw-shaped' tail-tips were observed in the mucoid strain. Crystalline material was produced by the mucoid strain but only when plated on certain media.     

Enhancement of Extra Chromosomal Recombination in Somatic Cells by Affecting the Ratio of Homologous Recombination (HR) to Non-Homologous End Joining (NHEJ)

Advancements in somatic cell gene targeting have been slow due to the finite lifespan of somatic cells and the overall inefficiency of homologous recombination. The rate of homologous recombination is determined by mechanisms of DNA repair, and by the balance between homologous recombination (HR) and non-homologous end joining (NHEJ). A plasmid-to-plasmid, extra chromosomal recombination system was used to study the effects of the manipulation of molecules involved in NHEJ (Mre11, Ku70/80, and p53) on HR/NHEJ ratios. In addition, the effect of telomerase expression, cell synchrony, and DNA nuclear delivery was examined. While a mutant Mre11 and an anti-Ku aptamer did not significantly affect the rate of NHEJ or HR, transient expression of a p53 mutant increased overall HR/NHEJ by 2.5 fold. However, expression of the mutant p53 resulted in increased aneuploidy of the cultured cells. Additionally, we found no relationship between telomerase expression and changes in HR/NHEJ. In contrast, cell synchrony by thymidine incorporation did not induce chromosomal abnormalities, and increased the ratio of HR/NHEJ 5-fold by reducing the overall rate of NHEJ. Overall our results show that attempts at reducing NHEJ by use of Mre11 or anti-Ku aptamers were unsuccessful. Cell synchrony via thymidine incorporation, however, does increase the ratio of HR/NHEJ and this indicates that this approach may be of use to facilitate targeting in somatic cells by reducing the numbers of colonies that need to be analyzed before a HR is identified.