Macroscopic Phase Coherence of Defective Vortex Lattices in Two Dimensions

The superfluid density is calculated theoretically for incompressible vortex lattices in two dimensions that have isolated dislocations quenched in by a random arrangement of pinned vortices. The latter are assumed to be sparse and to be fixed to material defects. It is shown that the pinned vortices act to confine a single dislocation of the vortex lattice along its glide plane. Plastic creep of the two-dimensional vortex lattice is thereby impeded, and macroscopic phase coherence results at low temperature in the limit of a dilute concentration of quenched-in dislocations.Comment: 18 pages, 1 figure, 1 table, new title, submitted to Physical Review

KCNMA1 Encoded Cardiac BK Channels Afford Protection against Ischemia-Reperfusion Injury

Mitochondrial potassium channels have been implicated in myocardial protection mediated through pre-/postconditioning. Compounds that open the Ca2+-and voltage-activated potassium channel of big-conductance (BK) have a pre-conditioninglike effect on survival of cardiomyocytes after ischemia/reperfusion injury. Recently, mitochondrial BK channels (mitoBKs) in cardiomyocytes were implicated as infarct-limiting factors that derive directly from the KCNMA1 gene encoding for canonical BKs usually present at the plasma membrane of cells. However, some studies challenged these cardio-protective roles of mitoBKs. Herein, we present electrophysiological evidence for paxilline- and NS11021-sensitive BK-mediated currents of 190 pS conductance in mitoplasts from wild-type but not BK-/- cardiomyocytes. Transmission electron microscopy of BK-/- ventricular muscles fibres showed normal ultra-structures and matrix dimension, but oxidative phosphorylation capacities at normoxia and upon re-oxygenation after anoxia were significantly attenuated in BK-/- permeabilized cardiomyocytes. In the absence of BK, post-anoxic reactive oxygen species (ROS) production from cardiomyocyte mitochondria was elevated indicating that mitoBK fine-tune the oxidative state at hypoxia and reoxygenation. Because ROS and the capacity of the myocardium for oxidative metabolism are important determinants of cellular survival, we tested BK-/- hearts for their response in an ex-vivo model of ischemia/reperfusion (I/R) injury. Infarct areas, coronary flow and heart rates were not different between wild-type and BK-/- hearts upon I/R injury in the absence of ischemic pre-conditioning (IP),but differed upon IP. While the area of infarction comprised 28 +/- 3% of the area at risk in wild-type, it was increased to 58 +/- 5% in BK-/- hearts suggesting that BK mediates the beneficial effects of IP. These findings suggest that cardiac BK channels are important for proper oxidative energy supply of cardiomyocytes at normoxia and upon re-oxygenation after prolonged anoxia and that IP might indeed favor survival of the myocardium upon I/R injury in a BK-dependent mode stemming from both mitochondrial post-anoxic ROS modulation and non-mitochondrial localizations

Unraveling compacted graphite evolution during solidification of cast iron using in-situ synchrotron X-ray tomography

In spite of many years of research, the physical phenomena leading to the evolution of compacted graphite (CG) during solidification is still not fully understood. In particular, it is unknown how highly branched CG aggregates form and evolve in the semi-solid, and how local microstructural variations at micrometer length scale affect this growth process. We present here the first time-resolved synchrotron tomography combined with a bespoke high-temperature environmental cell that allows direct observation of the evolution of CG and relates this dynamic process to the local surrounding microstructures in a cast iron sample during repeated melting and solidification. Distinct processes are identified for the formation of CG involving the nucleation, growth, development of branches and interconnection of graphite particles, ultimately evolving into highly branched graphite aggregates with large sizes and low sphericities. CG is found to nucleate with a spheroidal or a plate-like shape, developing branches induced by high carbon concentration, e.g. thin melt channels. Additionally, CG grows much faster than spheroidal graphite during subsequent cooling in solid state. The direct visualization of the dynamic solidification process provides unprecedented new insights into formation mechanisms of CG and correlating factors such as local microstructural variations, and guides the development of CG iron solidification models

Paxilline and NS11021 sensitive mitoBK channels give rise to a 190 pS conductance, which is absent in BK-negative mitoplasts.

<p>(<b>A1+2</b>) Expression analysis of BK channels mitochondrial protein fractions of adult heart (A1) and cardiac myocytes (A2) from BK^−/− and litter-mate BK^+/+ mice. Immune-reactive bands corresponding to the predicted molecular weight (approx. 120 kDa) of BK channels were detected only in mitochondrial protein fractions derived from BK^+/+ hearts and cardiac myocytes (red arrow), whereas mitochondrial lysates from BK^−/− tissues remained BK-negative. By identifying cytochrome c oxidase IV (COX IV) or heat shock protein 60 (hsp60) equal loading of the samples was confirmed. A fluorescent protein marker was used to estimate the sizes of the respective proteins (not shown). (<b>B</b>) Four different conductances were observed in mitoplasts from cardiomyocytes in a voltage step protocol with 2 seconds at +80 mV followed by 3 seconds at holding potential (−50 mV). Internal to external potassium ratio was 130∶10 mmol/l during the experiment. The magnitude of the occurring conductances under these conditions was calculated to approx. 370, 190, 120 and 60 pS. The figure displays individual representative traces of different patches which show a specific activity at the recorded time. Arrows indicate open state. (<b>C</b>) The relative frequency over 3 minutes of recording of the 190 pS (resembling BK K⁺-currents) conductance decreased from 29%±8% in BK^+/+ mice to 0% in BK^−/− mice. NS11021 increased the incidence of the 190 pS conductance to 41±3%, whereas the BK opener had no effect on BK-negative mitoplasts and paxilline reduced the incidence to 6±5% in BK^+/+ mitoplasts (number of single measurements was n = 17 for BK^+/+ and n = 23 for BK^−/−, number of mitoplasts preparations was four for each group). Statistical analyses were performed on BK^+/+ mitoplasts recorded in the untreated (basal) versus treated states (paxilline or NS11021). Additionally, all three conditions (basal, paxilline, NS11021) were tested for significant differences between the two genotypes (*P<0.05, **P<0.01). (<b>D</b>) Single channel analysis of an individual trace of a 190 pS conductance. The histogram with Gaussian fit results in a conductance of 192 pS. Additionally, slope conductance was determined by linear fit of current amplitude <i>versus</i> voltage confirming a conductance of 190 pS. (<b>E</b>) When assuming an easy two state model open probability can be calculated by idealization of channel openings and analysis of dwell times. This results in an open probability of 0.79 at 80 mV.</p

Loss of myocardial ischemic preconditioning in BK^−/− hearts.

<p>(<b>A</b>) Schematic illustration of the protocols used for the assessment of I/R injury in isolated, perfused hearts of BK^+/+ and BK^−/− mice. CTRL indicates a control protocol with 33 min global zero-flow ischemia followed by 60 min reperfusion and IP denotes an ischemic preconditioning protocol consisting of 2 extra cycles of 5 min ischemia and 5 min reperfusion preceding the global ischemic insult. (<b>B</b>) Effects of CTRL and IP protocol on post-ischemic coronary flow rate normalized to heart weight during reperfusion (upper), with each point depicting mean values ± SEM of the preceding 5 min recording. Coronary flow is significantly different as tested by Two-way ANOVA. Lower panel shows that IP improves coronary flow in the BK^+/+ but not in the BK^−/− group as evidenced by increased perfusate volume at reperfusion (area under the curve from the upper panel) at the time interval from 30 to 45 min and from 45 min to 60 min (ns = non-significant, *P<0.05 for CTRL BK^+/+<i>versus</i> IP BK^+/+; Two-way ANOVA followed by a Bonferroni post-hoc test). (<b>C</b>) Effects of CTRL and IP protocol on post-ischemic heart rate in BK^+/+ and BK^−/− group. Each point depicts mean values ± SEM of the 15 min interval recording excluding rare extrasystolic beats. Due to multiple sustained arrhythmias in the first 30 min of reperfusion, heart rate could not be reliably measured at the interval from 0–30 min (no differences between genotypes). Heart rate of BK^+/+ hearts is lower in the IP than in the CTRL group (*P<0.05 CTRL BK^+/+<i>versus</i> IP BK^+/+; Two-way ANOVA followed by a Bonferroni post-hoc test). (<b>D</b>) Effects of CTRL and IP protocol on infarct size in BK^+/+ and BK^−/− groups (upper panel). Infarct size is comparable between BK^+/+ and BK^−/− hearts in the CTRL group, but IP failed to protect BK^−/− hearts resulting in smaller infarct sizes of BK^+/+ hearts (**P<0.01; One-way ANOVA followed by Tukey’s multiple comparison test). All values are means ± SEM. Data from male and female BK^+/+ and accordingly BK^−/− hearts were pooled since sub-group analyses revealed that differences in the infarct sizes did not depend on sex. Lower panels demonstrate representative images of myocardial sections stained with tetrazolium chloride where red color indicates viable tissue and un-stained pale color demarcates infarcted areas.</p

Mitochondrial respiratory responses in mouse left heart ventricular fibres.

<p>O₂-consumption of permeabilized BK^+/+ fibres (blue bars) and fibres isolated from BK^−/− hearts (red bars) were measured by applying an <i>in vitro</i> model of I/R at normoxia and reo-xygenation (both at 21% O₂) upon 60 min of anoxia (by a N₂ gassing system). For a representative original recording trace please refer to Figure S2 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0103402#pone.0103402.s001" target="_blank">File S1</a>. (<b>A</b>) Coupled state 3 respiratory rate (OXPHOS) with complex I (CI) substrates malate (2 mmol/l) and glutamate (10 mmol/l) in the presence of ADP (5 mmol/l). (<b>B</b>) Cumulative OXPHOS of CI and II upon subsequent addition of succinate (10 mmol/l) to (A) for a supply of electrons to complex II (CII). OXPHOS of CI and II after 5 min (OXPHOS₅) and after 60 min (OXPHOS₆₀) of anoxia are shown. (<b>C</b>) Ratio of respiration upon addition of cytochrome c (CYTC) 5 min after 60 min anoxia compared to steady state respiratory flux rate before anoxia as a test for intactness of the IMM. (<b>D</b>) Isolated activity of complex IV (cytochrome c oxidase (COX)) with redox substrates ascorbate (2 mmol/l) and TMPD (5 mmol/l) in the presence of complex III blocker Antimycin A (2 µmol/l). (<b>E</b>) Ratio of OXPHOS to COX activity under fully oxygenated conditions showing loss of COX excess capacity in BK^−/− as the ratio approaches 1.0 revealing an insufficient reserve capacity to produce energy in mitoBK-deficient fibres. Data are mean ± SEM with n = 6 for BK^+/+ and n = 9 for BK^−/− with ns = non-significant and **P<0.01 significantly different compared to BK^+/+ (Fig. 2A, C, D two-tailed paired t-test). *P<0.05, **P<0.01, significantly different compared to BK^+/+ within the respective condition (Fig. 2B).</p