Atrial fibrillation ablation: a single center comparison between remote magnetic navigation, cryoballoon and conventional manual pulmonary vein isolation

Background

The aim of the study was to compare in our center the effect of different ablation techniques on intermediate term freedom from atrial fibrillation (AF) or atrial tachycardia (AT) in patients affected by refractory AF.

Methods and Results

We retrospectively selected 94 patients who underwent AF ablation in our electrophysiological laboratory from June 2007 to December 2009. 29 patients underwent manual circumferential pulmonary vein isolation (mCPVI), 35 underwent remote magnetic navigation assisted CPVI (rmtCPVI) and 30 cryoballoon CPVI (cCPVI). Antiarrhythmic drugs were systematically stopped 2 months after the procedure (end of the "blanking period").At a mean follow-up of 12,64 ± 6,41 months (range 2-31), the success rate for mCPVI group was 65.5% (19 patients), 66.7 % (20 patients) for the rmtCPVI group and 65.7 % (23 patients) for the cCPVI group (p = 0.625). Procedural and fluoroscopy times were significantly reduced in the cCPVI group (both p < 0.001). Univariate Cox regression showed that no clinical variables were independently associated with recurrence.

Conclusions

In our center''s experience cCPVI and rmtCPVI have been demonstrated to be as effective as mCPVI. cCPVI seemed to be associated with lower procedural and fluoroscopy times.     

High-resolution cryo-EM maps show the nucleotide binding pocket of KIF1A in open and closed conformations

Kinesin is an ATP-driven microtubule (MT)-based motor fundamental to organelle transport. Although a number of kinesin crystal structures have been solved, the structural evidence for coupling between the bound nucleotide and the conformation of kinesin is elusive. In addition, the structural basis of the MT-induced ATPase activity of kinesin is not clear because of the absence of the MT in the structure. Here, we report cryo-electron microscopy structures of the monomeric kinesin KIF1A-MT complex in two nucleotide states at about 10 A resolution, sufficient to reveal the secondary structure. These high-resolution maps visualized clear structural changes that suggest a mechanical pathway from the nucleotide to the neck linker via the motor core rotation. In addition, new nucleotide binding pocket conformations are observed that are different from X-ray crystallographic structures; it is closed in the 5'-adenylyl-imidodiphosphate state, but open in the ADP state. These results suggest a structural model of biased diffusion movement of monomeric kinesin motor.     

Multidrug and Toxic Compound Extrusion-Type Transporters Implicated in Vacuolar Sequestration of Nicotine in Tobacco Roots

Nicotine is a major alkaloid accumulating in the vacuole of tobacco (Nicotiana tabacum), but the transporters involved in the vacuolar sequestration are not known. We here report that tobacco genes (NtMATE1 and NtMATE2) encoding transporters of the multidrug and toxic compound extrusion (MATE) family are coordinately regulated with structural genes for nicotine biosynthesis in the root, with respect to spatial expression patterns, regulation by NIC regulatory loci, and induction by methyl jasmonate. Subcellular fractionation, immunogold electron microscopy, and expression of a green fluorescent protein fusion protein all suggested that these transporters are localized to the vacuolar membrane. Reduced expression of the transporters rendered tobacco plants more sensitive to the application of nicotine. In contrast, overexpression of NtMATE1 in cultured tobacco cells induced strong acidification of the cytoplasm after jasmonate elicitation or after the addition of nicotine under nonelicited conditions. Expression of NtMATE1 in yeast (Saccharomyces cerevisiae) cells compromised the accumulation of exogenously supplied nicotine into the yeast cells. The results imply that these MATE-type proteins transport tobacco alkaloids from the cytosol into the vacuole in exchange for protons in alkaloid-synthesizing root cells.Alkaloids are a chemically diverse group of low-molecular weight, nitrogen-containing secondary metabolites with characteristic toxicity and pharmacological activity and may function in the chemical defense of plants against herbivores and pathogens (Facchini, 2001; Steppuhn et al., 2004). Natural hydrophilic products, including alkaloids, are usually stored in the vacuole, which appears to be especially adapted to the bulk storage of chemicals for defensive functions. Due to its nitrogen atom(s), an alkaloid can be protonated and is a base. Because several weakly basic alkaloids, such as nicotine, are present in the lipophilic non-charged form in slightly alkaline solutions, a portion of these alkaloids in the cytoplasm may pass through the tonoplast by simple diffusion. An ion-trap mechanism has been proposed to drive an apparent uphill transport of weakly basic alkaloids against a concentration gradient, in which alkaloids are protonated in the acidic vacuole to become membrane-impermeable hydrophilic molecules (Wink and Roberts, 1998). This trapping mechanism removes transport-competent “free” molecules and thus enables the uphill transport process. As attractive as this model is, it is not known whether and how much the actual vacuolar transport of weakly basic alkaloids depends on the trapping mechanism. In contrast, other alkaloids, which are charged under cytosolic pH conditions, are thought to pass through the tonoplast via a carrier-mediated mechanism (Deus-Newmann and Zenk, 1986; Otani et al., 2005).Nicotine is a major alkaloid synthesized in most commercial varieties of tobacco (Nicotiana tabacum). In tobacco, nicotine is synthesized exclusively in the root and distributed throughout the plant via the xylem, concentrating in the young tissues of aerial parts (Hashimoto and Yamada, 1995; Baldwin, 2001). As much as 60 mm of nicotine accumulates in the vacuoles of the leaf epidermal cells at the tip (Lochmann et al., 2001). Putrescine N-methyltransferase (PMT) catalyzes the first committed step in the nicotine-specific pathway, and a PIP-family reductase, called A622, was also suggested to function in a late step in nicotine biosynthesis (Hibi et al., 1994; Shoji et al., 2000a, 2000b; DeBoer et al., 2009; Kajikawa et al., 2009). PMT and A622 proteins are specifically expressed in the same cell types in the root (Shoji et al., 2000a, 2002). Both enzymes were abundant in the endodermis and cortex cells of the root tips, whereas in the differentiated region of the root, the outermost layer of the cortex and parenchyma cells surrounding the xylem in the vascular bundle contained these proteins. These localization patterns not only substantiated root-specific nicotine biosynthesis but also suggested nicotine synthesis to be intimately associated with the xylem-based transport.Nicotine biosynthesis is positively regulated by the jasmonate-signaling cascade involving the COI1 F-box protein and JAZ repressors (Paschold et al., 2007; Shoji et al., 2008) and by the NIC regulatory loci that specifically control the gene expression of all enzymes known to be involved in the biosynthesis (Legg, 1984; Hibi et al., 1994; Reed and, Jelesko, 2004; Cane et al., 2005; Heim et al., 2007; Katoh et al., 2007). In flavonoid biosynthesis, regulatory genes coordinately regulate not only enzyme genes but also transporter genes responsible for intracellular transport of the metabolites (Koes et al., 2005). In this study, we identified two related tobacco transporters that are coordinately regulated by the NIC loci with nicotine biosynthetic enzymes. Our results suggest that these transporters promote the uptake of nicotine and related alkaloids into the vacuole by using a H⁺-gradient across the tonoplast in the alkaloid-synthesizing root cells.     

Ectomycorrhizal Inocybe species associate with the mycoheterotrophic orchid Epipogium aphyllum but not its asexual propagules

Background and Aims

Epipogium aphyllum is a Eurasian achlorophyllous, mycoheterotrophic forest orchid. Due to its rarity, it is often protected, and its biology is poorly known. The identity and pattern of colonization of fungal associates providing carbon to this orchid have not been studied previously.

Methods

Using samples from 34 individuals from 18 populations in Japan, Russia and France, the following were investigated: (a) colonization patterns of fungal associates of E. aphyllum by microscopy; (b) their identity by PCR amplification of nuclear ribosomal ITS carried out on rhizome fragments and hyphal pelotons.

Results and Conclusions

Microscopic investigations revealed that thick rhizomes were densely colonized by fungi bearing clamp-connections and dolipores, i.e. basidiomycetes. Molecular analysis identified Inocybe species as exclusive symbionts of 75 % of the plants investigated and, more rarely, other basidiomycetes (Hebeloma, Xerocomus, Lactarius, Thelephora species). Additionally, ascomycetes, probably endophytes or parasites, were sometimes present. Although E. aphyllum associates with diverse species from Inocybe subgenera Mallocybe and Inocybe sensu stricto, no evidence for cryptic speciation in E. aphyllum was found. Since basidiomycetes colonizing the orchid are ectomycorrhizal, surrounding trees are probably the ultimate carbon source. Accordingly, in one population, ectomycorrhizae sampled around an individual orchid revealed the same fungus on 11·2 % of tree roots investigated. Conversely, long, thin stolons bearing bulbils indicated active asexual multiplication, but these propagules were not colonized by fungi. These findings are discussed in the framework of ecology and evolution of mycoheterotrophy.Key words: Asexual multiplication, ectomycorrhizae, Epipogium, Inocybe, mycoheterotrophy, orchid mycorrhizae, specificity, symbiont transmission     

Characterization of extracellular DNA production and flocculation of the marine photosynthetic bacterium <Emphasis Type="Italic">Rhodovulum sulfidophilum</Emphasis>

The marine photosynthetic bacterium Rhodovulum sulfidophilum produces extracellular nucleic acids involved in its flocculation. Previously, we showed that the RNA fraction of these extracellular nucleic acids released into the culture medium contains mainly non-aminoacylated fully mature-sized tRNAs and fragments of 16S and 23S rRNAs. Here, we report the characterization of extracellular DNA itself and its production during cultivation. No differences were detected in nucleotide sequence between the intracellular DNA and extracellular soluble DNA on Southern blotting. Whole intracellular DNA seemed to be released from the cell. The bacterial floc was degraded by deoxyribonuclease or ribonuclease treatment, indicating that at least the extracellular DNA and RNAs in the floc are involved in the maintenance of the floc. When cultivated in nutritionally rich medium, the bacteria formed small flocs and produced large amounts of extracellular DNA, which were solubilized in the medium. In nutritionally poor medium, however, huge flocs of cells appeared and almost no extracellular soluble DNA was observed in the medium. As the floc was degraded by deoxyribonuclease treatment, it seems likely that the extracellular soluble DNA observed in the rich medium may be incorporated into the large floc and play a role in floc maintenance in poor medium. Addition of an inhibitor of quorum sensing, α-cyclodextrin, inhibited huge floc maintenance in the nutritionally poor medium. In the presence of α-cyclodextrin, the floc was rapidly degraded and extracellular soluble DNA production increased.     

A redox‐linked novel pathway for arsenic‐mediated RET tyrosine kinase activation

We examined the biochemical effects of arsenic on the activities of RET proto‐oncogene (c‐RET protein tyrosine kinases) and RET oncogene (RET‐MEN2A and RET‐PTC1 protein tyrosine kinases) products. Arsenic activated c‐RET kinase with promotion of disulfide bond‐mediated dimerization of c‐RET protein. Arsenic further activated RET‐MEN2A kinase, which was already 3‐ to 10‐fold augmented by genetic mutation compared with c‐RET kinase activity, with promotion of disulfide bond‐mediated dimerization of RET‐MEN2A protein (superactivation). Arsenic also increased extracellular domain‐deleted RET‐PTC1 kinase activity with promotion of disulfide bond‐mediated dimerization of RET‐PTC1 protein. Arsenic increased RET‐PTC1 kinase activity with cysteine 365 (C365) replaced by alanine with promotion of dimer formation but not with cysteine 376 (C376) replaced by alanine. Our results suggest that arsenic‐mediated regulation of RET kinase activity is dependent on conformational change of RET protein through modulation of a special cysteine sited at the intracellular domain in RET protein (relevant cysteine of C376 in RET‐PTC1 protein). Moreover, arsenic enhanced the activity of immunoprecipitated RET protein with increase in thiol‐dependent dimer formation. As arsenic (14.2 µM) was detected in the cells cultured with arsenic (100 µM), direct association between arsenic and RET in the cells might modulate dimer formation. Thus, we demonstrated a novel redox‐linked mechanism of activation of arsenic‐mediated RET proto‐oncogene and oncogene products. J. Cell. Biochem. 110: 399–407, 2010. © 2010 Wiley‐Liss, Inc.     

Human MDR1 and MRP1 recognize berberine as their transport substrate

To examine whether human ATP-binding cassette (ABC) transporters play a role in the detoxification of plant alkaloid berberine, we investigated berberine transport using multidrug resistance protein1 (MDR1) and multidrug resistance-associated protein1 (MRP1). Cells expressing MDR1 or MRP1 accumulated less berberine. Berberine accumulation depended on the cellular ATP level, and was reversed by typical inhibitors of MDR1, suggesting that human MDR1 and MRP1 directly efflux berberine as their substrate.