Benchmark solution for the prediction of temperature distributions during radiofrequency ablation of cardiac tissue

Several studies on radiofrequency (RF) ablation are aimed at accurately predicting tissue temperature distributions by numerical solution of the bioheat equation. This paper describes the development of a solution that can serve as a benchmark for subsequent numerical solutions. The solution was obtained using integral transforms and evaluated using a C program. Temperature profiles were generated at various times and for different convection coefficients. In addition, a numerical model was developed using the same assumptions made in obtaining the benchmark solution. Comparison of surface and axial temperature profiles shows that the two solutions match very closely, cross validating the numerical methods used in evaluating both solutions.     

Iron does not cause arrhythmias in the guinea pig model of transfusional iron overload

Cardiac events, including heart failure and arrhythmias, are the leading cause of death in patients with beta thalassemia. Although cardiac arrhythmias in humans are believed to result from iron overload, excluding confounding factors in the human population is difficult. The goal of the current study was to determine whether cardiac arrhythmias occurred in the guinea pig model of secondary iron overload. Electrocardiograms were recorded by using surgically implanted telemetry devices in guinea pigs loaded intraperitoneally with iron dextran (test animals) or dextran alone (controls). Loading occurred over approximately 6 wk. Electrocardiograms were recorded for 1 wk prior to loading, throughout loading, and for approximately 4 wk after loading was complete. Cardiac and liver iron concentrations were significantly increased in the iron-loaded animals compared with controls and were in the range of those reported for humans with thalassemia. Arrhythmias were rare in both iron-loaded and control guinea pigs. No life-threatening arrhythmias were detected in either group. These data suggest that iron alone may be insufficient to cause cardiac arrhythmias in the iron-loaded guinea pig model and that arrhythmias detected in human patients with iron overload may be the result of a complex interplay of factors.     

Clocking out: modeling phage-induced lysis of Escherichia coli

Phage lambda lyses the host Escherichia coli at a precisely scheduled time after induction. Lysis timing is determined by the action of phage holins, which are small proteins that induce hole formation in the bacterium's cytoplasmic membrane. We present a two-stage nucleation model of lysis timing, with the nucleation of condensed holin rafts on the inner membrane followed by the nucleation of a hole within those rafts. The nucleation of holin rafts accounts for most of the delay of lysis after induction. Our simulations of this model recover the accurate lysis timing seen experimentally and show that the timing accuracy is optimal. An enhanced holin-holin interaction is needed in our model to recover experimental lysis delays after the application of membrane poison, and such early triggering of lysis is possible only after the inner membrane is supersaturated with holin. Antiholin reduces the delay between membrane depolarization and lysis and leads to an earlier time after which triggered lysis is possible.     

Impacts of T-Phylloplanin gene knockdown and of Helianthus and Datura phylloplanins on Peronospora tabacina spore germination and disease potential

T-phylloplanin proteins secreted to aerial surfaces of tobacco (Nicotiana tabacum) by short procumbent trichomes inhibit spore germination and blue mold disease caused by the oomycete pathogen Peronospora tabacina. Many other plants were found to contain water-washed leaf surface proteins (phylloplanins), but the functions and properties of these are not known. Here we extend earlier evidence for the antifungal activity of T-phylloplanins using a reverse genetics approach. RNA interference of the T-phylloplanin gene in tobacco 'T.I. 1068' resulted in loss of T-phylloplanin mRNA and protein, loss of in vitro spore germination inhibition activity, and leaf infection inhibition activity of leaf water washes from RNA interference plants, and young knockdown plants were susceptible to disease. The glycoprotein character, adaxial-leaf-surface enrichment of, and renewability of T-phylloplanins are also described. We also report that leaf water washes of sunflower (Helianthus annuus) and jimson weed (Datura metel), but not soybean (Glycine max), like that of tobacco, possess ProteinaseK- and boiling-sensitive P. tabacina spore germination and tobacco leaf infection inhibition activities. Results establish that T-phylloplaninins of tobacco are active in P. tabacina inhibition, and indicate that leaf surface proteins of certain non-Nicotiana species that are not susceptible to P. tabacina disease can inhibit germination of spores of this oomycete pathogen and inhibit tobacco leaf infection by this pathogen.     

Local polarity and hydrogen bonding inside the Sec14p phospholipid-binding cavity: high-field multi-frequency electron paramagnetic resonance studies

Sec14p promotes the energy-independent transfer of either phosphatidylinositol (PtdIns) or phosphatidylcholine (PtdCho) between lipid bilayers in vitro and represents the major PtdIns/PtdCho transfer protein in the budding yeast Saccharomyces cerevisiae. Herein, we employ multi-frequency high-field electron paramagnetic resonance (EPR) to analyze the electrostatic and hydrogen-bonding microenvironments for series of doxyl-labeled PtdCho molecules bound by Sec14p in a soluble protein-PtdCho complex. A structurally similar compound, 5-doxyl stearic acid dissolved in a series of solvents, was used for experimental calibration. The experiments yielded two-component rigid limit 130- and 220-GHz EPR spectra with excellent resolution in the gx region. Those components were assigned to hydrogen-bonded and nonhydrogen-bonded nitroxide species. Partially resolved 130-GHz EPR spectra from n-doxyl-PtdCho bound to Sec14p were analyzed using this two-component model and allowed quantification of two parameters. First, the fraction of hydrogen-bonded nitroxide species for each n-doxyl-PtdCho was calculated. Second, the proticity profile along the phospholipid-binding cavity of Sec14p was characterized. The data suggest the polarity gradient inside the Sec14p cavity is a significant contributor to the driving molecular forces for extracting a phospholipid from the bilayer. Finally, the enhanced g-factor resolution of EPR at 130 and 220 GHz provides researchers with a spectroscopic tool to deconvolute two major contributions to the x-component of the nitroxide g-matrix: hydrogen-bond formation and local electrostatic effects.     

Formation of a multiple protein complex on the adenovirus packaging sequence by the IVa2 protein

During adenovirus virion assembly, the packaging sequence mediates the encapsidation of the viral genome. This sequence is composed of seven functional units, termed A repeats. Recent evidence suggests that the adenovirus IVa2 protein binds the packaging sequence and is involved in packaging of the genome. Study of the IVa2-packaging sequence interaction has been hindered by difficulty in purifying the protein produced in virus-infected cells or by recombinant techniques. We report the first purification of a recombinant untagged version of the adenovirus IVa2 protein and characterize its binding to the packaging sequence in vitro. Our data indicate that there is more than one IVa2 binding site within the packaging sequence and that IVa2 binding to DNA requires the A-repeat consensus, 5'-TTTG-(N(8))-CG-3'. Furthermore, we present evidence that IVa2 forms a multimeric complex on the packaging sequence. These data support a model in which adenovirus DNA packaging occurs via the formation of a IVa2 multiprotein complex on the packaging sequence.     

Character displacement and the evolution of mate choice: an artificial neural network approach

Interactions with heterospecifics can promote the evolution of divergent mating behaviours between populations that do and do not occur with heterospecifics. This process--reproductive character displacement--potentially results from selection to minimize the risk of mating with heterospecifics. We sought to determine whether heterospecific interactions lead to divergence of female preferences for aspects of conspecific male signals. We used artificial neural network models to simulate a mate recognition system in which females co-occur with different heterospecifics in different populations. Populations that evolved conspecific recognition in the presence of different heterospecifics varied in their preferences for aspects of conspecific male signals. When we tested networks for their preferences of conspecific versus heterospecific signals, however, we found that networks from allopatric populations were usually able to select against heterospecifics. We suggest that female preferences for aspects of conspecific male signals can result in a concomitant reduction in the likelihood that females will mate with heterospecifics. Consequently, even females in allopatry may discriminate against heterospecific mates depending on the nature of their preferences for conspecifics. Such a pattern could potentially explain cases where reproductive character displacement is expected, but not observed.     

Structural and functional analysis of MiD51, a dynamin receptor required for mitochondrial fission

Mitochondrial fission is important for organelle transport, inheritance, and turnover, and alterations in fission are seen in neurological disease. In mammals, mitochondrial fission is executed by dynamin-related protein 1 (Drp1), a cytosolic guanosine triphosphatase that polymerizes and constricts the organelle. Recruitment of Drp1 to mitochondria involves receptors including Mff, MiD49, and MiD51. MiD49/51 form foci at mitochondrial constriction sites and coassemble with Drp1 to drive fission. Here, we solved the crystal structure of the cytosolic domain of human MiD51, which adopts a nucleotidyltransferase fold. Although MiD51 lacks catalytic residues for transferase activity, it specifically binds guanosine diphosphate and adenosine diphosphate. MiD51 mutants unable to bind nucleotides were still able to recruit Drp1. Disruption of an additional region in MiD51 that is not part of the nucleotidyltransferase fold blocked Drp1 recruitment and assembly of MiD51 into foci. MiD51 foci are also dependent on the presence of Drp1, and after scission they are distributed to daughter organelles, supporting the involvement of MiD51 in the fission apparatus.