A 2-4 keV multilayer mirrored channel for the NIF Dante system.

During inertial confinement fusion experiments at the National Ignition Facility (NIF), a capsule filled with deuterium and tritium (DT) gas, surrounded by a DT ice layer and a high-density carbon ablator, is driven to the temperature and densities required to initiate fusion. In the indirect method, 2 MJ of NIF laser light heats the inside of a gold hohlraum to a radiation temperature of 300 eV; thermal x rays from the hohlraum interior couple to the capsule and create a central hotspot at tens of millions degrees Kelvin and a density of 100-200 g/cm3. During the laser interaction with the gold wall, m-band x rays are produced at ∼2.5 keV; these can penetrate into the capsule and preheat the ablator and DT fuel. Preheat can impact instability growth rates in the ablation front and at the fuel-ablator interface. Monitoring the hohlraum x-ray spectrum throughout the implosion is, therefore, critical; for this purpose, a Multilayer Mirror (MLM) with flat response in the 2-4 keV range has been installed in the NIF 37° Dante calorimeter. Precision engineering and x-ray calibration of components mean the channel will report 2-4 keV spectral power with an uncertainty of ±8.7%.

[Magnesium deficiency and therapy in cardiac arrhythmias: recommendations of the German Society for Magnesium Research]. / Magnesiummangel und Magnesiumtherapie bei Herzrhythmusstörungen. Empfehlungen der Gesellschaft für Magnesium-Forschung e. V.

Aim of the recommendations of the German Society for Magnesium Research: Recognition and compensation of magnesium deficiency in patients with risk factors for cardiac arrhythmias or manifest rhythm disturbances. Prevention of arrhythmias by administration of magnesium. Therapeutic administration of magnesium in patients with arrhythmias with and without magnesium deficiency. The current state of knowledge claims for considering the status of magnesium and the possibility of a therapeutic intervention with magnesium within the concept of the treatment of cardiovascular diseases. The use of magnesium as single agent or as an adjunct to other therapeutic actions in the prevention and therapy of cardiac arrhythmias can be effective and, in case of oral administration, very safe. In case of parenteral administration, it is important to use adequate doses, monitor cardiovascular and neuromuscular parameters and to consider contraindications.

Early-time symmetry tuning in the presence of cross-beam energy transfer in ICF experiments on the National Ignition Facility.

On the National Ignition Facility, the hohlraum-driven implosion symmetry is tuned using cross-beam energy transfer (CBET) during peak power, which is controlled by applying a wavelength separation between cones of laser beams. In this Letter, we present early-time measurements of the instantaneous soft x-ray drive at the capsule using reemission spheres, which show that this wavelength separation also leads to significant CBET during the first shock, even though the laser intensities are 30× smaller than during the peak. We demonstrate that the resulting early drive P2/P0 asymmetry can be minimized and tuned to <1% accuracy (well within the ±7.5% requirement for ignition) by varying the relative input powers between different cones of beams. These experiments also provide time-resolved measurements of CBET during the first 2 ns of the laser drive, which are in good agreement with radiation-hydrodynamics calculations including a linear CBET model.

TRP channels in disease.

The transient receptor potential (TRP) channels are a large family of proteins with six main subfamilies termed the TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), and TRPA (ankyrin) groups. The sheer number of different TRPs with distinct functions supports the statement that these channels are involved in a wide range of processes ranging from sensing of thermal and chemical signals to reloading intracellular stores after responding to an extracellular stimulus. Mutations in TRPs are linked to pathophysiology and specific diseases. An understanding of the role of TRPs in normal physiology is just beginning; the progression from mutations in TRPs to pathophysiology and disease will follow. In this review, we focus on two distinct aspects of TRP channel physiology, the role of TRP channels in intracellular Ca2+ homeostasis, and their role in the transduction of painful stimuli in sensory neurons.

Implementation of evidence-based therapy in patients with systolic heart failure from 1998-2000.

BACKGROUND: In recent years, the incidence of systolic heart failure has increased. Besides a complete revascularization, guideline-based medication represents the most effective therapeutic approach. AIM: Analysis of adherence of guideline-recommended and actual medication during inpatient cardiac rehabilitation as well as under subsequent outpatient conditions. METHODS: From 01/1998 to 12/ 2000, 1346 consecutive patients (64 +/- 10 years, 73% male, LVEF 36.3 +/- 8%, 88% ischemic, 6.7% valvular cardiomyopathy, 5.3% other causes, 11.8% atrial fibrillation) were included in a singlecenter prospective register. Medication was recorded at discharge and after the follow-up period of 731 +/- 215 days. Trends in prescription rates were analyzed based on nonparametric correlations (Spearman's-Rho). Changes in medication from in- to outpatient settings were analyzed using exact McNemar test. RESULTS: At discharge 75.3% (67.9%/68.9%/ 86.6% in 1998/1999/2000, p <0.001) of the patients were treated as recommended. This rate dropped to 68.3% at followup (p <0.0001). Mortality within the follow-up period was low (12.6%). CONCLUSION: It could be shown that from 1998 to 2000 inpatient guideline conformity was implementable adequately. Outpatient conformity was significantly lower. Although a high proportion of correctly prescribed CHF medication could be demonstrated, a further effort to improve guideline adherence in the management of heart failure patients is desirable.

Nuclear and cytosolic calcium are regulated independently.

Nuclear calcium (Ca(2+)) regulates a number of important cellular processes, including gene transcription, growth, and apoptosis. However, it is unclear whether Ca(2+) signaling is regulated differently in the nucleus and cytosol. To investigate this possibility, we examined subcellular mechanisms of Ca(2+) release in the HepG2 liver cell line. The type II isoform of the inositol 1,4,5-trisphosphate (InsP(3)) receptor (InsP(3)R) was expressed to a similar extent in the endoplasmic reticulum and nucleus, whereas the type III InsP(3)R was concentrated in the endoplasmic reticulum, and the type I isoform was not expressed. Ca(2+) signals induced by low InsP(3) concentrations started earlier or were larger in the nucleus than in the cytosol, indicating higher sensitivity of nuclear Ca(2+) stores for InsP(3). Nuclear InsP(3)R channels were active at lower InsP(3) concentrations than InsP(3)R from cytosol. Enriched expression of type II InsP(3)R in the nucleus results in greater sensitivity of the nucleus to InsP(3), thus providing a mechanism for independent regulation of Ca(2+)-dependent processes in this cellular compartment.

Characterization of the calcium-release channel/ryanodine receptor from zebrafish skeletal muscle.

Calcium (Ca2+)-mediated signaling is fueled by two sources for Ca2+: Ca2+ can enter through Ca2+ channels located in the plasma membrane and can also be released from intracellular stores. In the present study the intracellular Ca2+ release channel/ryanodine receptor (RyR) from zebrafish skeletal muscle was characterized. Two RyR isoforms could be identified using immunoblotting and single-channel recordings. Biophysical properties as well as the regulation by modulators of RyR, ryanodine, ruthenium red and caffeine, were measured. Comparison with other RyRs showed that the zebrafish RyRs have features observed with all RyRs described to date and thus, can serve as a model system in future genetic and physiological studies. However, some differences in the biophysical properties were observed. The slope conductance for both isoforms was higher than that of the mammalian RyR type 1 (RyR1) measured with divalent ions. Also, inhibition by millimolar Ca2+ concentrations of the RyR isoform that is inhibited by high Ca2+ concentrations (teleost alpha RyR isoform) was attenuated when compared to mammalian RyRs. Due to the widespread expression of RyR these findings have important implications for the interpretation of the role of the RyR in Ca2+ signaling when comparing zebrafish with mammalian physiology, especially when analyzing mutations underlying physiological changes in zebrafish.

Regulation of Ins(1,4,5)P3 receptor isoforms by endogenous modulators.

Three isoforms of the inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3] receptor have been identified. Each receptor isoform has been functionally characterized using many different techniques. Although these receptor isoforms possess high homology, interesting differences in their Ca2+ dependence, Ins(1,4,5)P3 sensitivity and subcellular distribution exist, implying distinct cellular roles. Indeed, interplay among the isoforms might be necessary for a cell to control spatial and temporal aspects of cytosolic Ca2+ signals, which are important for many cellular processes. In this review isoform-specific functions, primarily at the single-channel level, will be highlighted and these properties will be correlated with Ca2+ signals in intact cells.

Human disease: calcium signaling in polycystic kidney disease.

Polycystic kidney disease results from loss of function of either of two novel proteins, polycystin-1 or polycystin-2. Recent studies show that intracellular calcium signaling is important in kidney development, and define defects in this signaling pathway as the basis of cyst formation in polycystic kidney disease.

Conservation of localization patterns of IP(3) receptor type 1 in cerebellar Purkinje cells across vertebrate species.

The distribution of inositol 1,4,5-trisphosphate (IP(3)) receptor type 1 (IP(3)R1) protein was studied in the adult cerebella of six different vertebrate species, zebrafish, skate, claw frog, rat, hamster, and mouse. The receptor was found at high expression levels in Purkinje cells in all species examined using a subtype-specific polyclonal antiserum against IP(3)R1 and fluorescence immunocytochemistry. The immunoreactivity for IP(3)R1 was found intracellularly at high concentrations in dendrites and somata and at lower levels in axons of these cells. Despite the morphological and functional differences of the cerebella the staining patterns of IP(3)R1 labeling in Purkinje cells was preserved. This is notable because the cerebella were taken from organisms representing a large segment of vertebrate phylogenetic development. The high expression levels of IP(3)R1 in Purkinje cells were found independent of the degree of the formation of fissures and folia and of the degree of branching of Purkinje cell dendrites. The conservation of cerebellar structures not only at the cellular level but more importantly at the molecular level suggests that identical intracellular calcium signaling mechanisms are used in a number of species that represent different areas of phylogenetic development and specialization.

Reversible block of the calcium release channel/ryanodine receptor by protamine, a heparin antidote.

Channel activity of the calcium release channel from skeletal muscle, ryanodine receptor type 1, was measured in the presence and absence of protamine sulfate on the cytoplasmic side of the channel. Single-channel activity was measured after incorporating channels into planar lipid bilayers. Optimally and suboptimally calcium-activated calcium release channels were inactivated by the application of protamine to the cytoplasmic side of the channel. Recovery of channel activity was not observed while protamine was present. The addition of protamine bound to agarose beads did not change channel activity, implying that the mechanism of action involves an interaction with the ryanodine receptor rather than changes in the bulk calcium concentration of the medium. The block of channel activity by protamine could be reversed either by removal by perfusion with buffer or by the addition of heparin to the cytoplasmic side of the channel. Microinjection of protamine into differentiated C(2)C(12) mouse muscle cells prevented caffeine-induced intracellular calcium release. The results suggest that protamine acts on the ryanodine receptor in a similar but opposite manner from heparin and that protamine can be used as a potent, reversible inhibitor of ryanodine receptor activity.

Regulation of the type III InsP(3) receptor by InsP(3) and ATP.

Many hormones and neurotransmitters raise intracellular calcium (Ca(2+)) by generating InsP(3) and activating the inositol 1,4, 5-trisphosphate receptor (InsP(3)R). Multiple isoforms with distinct InsP(3) binding properties () have been identified (). The type III InsP(3)R lacks Ca(2+)-dependent inhibition, a property that makes it ideal for signal initiation (). Regulation of the type III InsP(3)R by InsP(3) and ATP was explored in detail using planar lipid bilayers. In comparison to the type I InsP(3)R, the type III InsP(3)R required a higher concentration of InsP(3) to reach maximal channel activity (EC(50) of 3.2 microM versus 0.5 microM for the types III and I InsP(3)R, respectively). However, the type III InsP(3)R did reach a 2.5-fold higher level of activity. Although activation by InsP(3) was isoform-specific, regulation by ATP was similar for both isoforms. In the presence of 2 microM InsP(3), low ATP concentrations (<6 mM) increased the open probability and mean open time. High ATP concentrations (>6 mM) decreased channel activity. These results illustrate the complex nature of type III InsP(3)R regulation. Enhanced channel activity in the presence of high InsP(3) may be important during periods of prolonged stimulation, whereas allosteric modulation by ATP may help to modulate intracellular Ca(2+) signaling.

Regulation of the type III InsP3 receptor and its role in beta cell function.

The type III inositol 1,4,5-trisphosphate receptor (InsP3R) is an important intracellular calcium (Ca2+) release channel in the pancreatic beta cell. Pancreatic beta cells secrete insulin following a characteristic change in membrane potential that leads to an increase in cytoplasmic Ca2+. Both extracellular Ca2+ and Ca2+ mobilized from InsP3-sensitive stores contribute to this increase. RIN-m5F cells, an insulin-secreting beta cell line, preferentially express the type III InsP3R. These cells have been useful in determining the regulatory properties of the type III InsP3R and the role of this isoform in an intact cell. The type III InsP3R is ideal for signal initiation because high cytoplasmic Ca2+ does not inhibit its activity. Altered insulin secretion, the result of changes in Ca2+ handling by the beta cell, has significant clinical consequences.

Regulation of type 1 inositol 1,4,5-trisphosphate-gated calcium channels by InsP3 and calcium: Simulation of single channel kinetics based on ligand binding and electrophysiological analysis.

Cytosolic calcium acts as both a coagonist and an inhibitor of the type 1 inositol 1,4,5-trisphosphate (InsP3)-gated Ca channel, resulting in a bell-shaped Ca dependence of channel activity (Bezprozvanny, I., J. Watras, and B.E. Ehrlich. 1991. Nature. 351:751-754; Finch, E.A., T.J. Turner, and S.M. Goldin. 1991. Science. 252: 443-446; Iino, M. 1990. J. Gen. Physiol. 95:1103-1122). The ability of Ca to inhibit channel activity, however, varies dramatically depending on InsP3 concentration (Combettes, L., Z. Hannaert-Merah, J.F. Coquil, C. Rousseau, M. Claret, S. Swillens, and P. Champeil. 1994. J. Biol. Chem. 269:17561-17571; Kaftan, E.J., B.E. Ehrlich, and J. Watras. 1997. J. Gen. Physiol. 110:529-538). In the present report, we have extended the characterization of the effect of cytosolic Ca on both InsP3 binding and InsP3-gated channel kinetics, and incorporated these data into a mathematical model capable of simulating channel kinetics. We found that cytosolic Ca increased the Kd of InsP3 binding approximately 3.5-fold, but did not influence the maximal number of binding sites. The ability of Ca to decrease InsP3 binding is consistent with the rightward shift in the bell-shaped Ca dependence of InsP3-gated Ca channel activity. High InsP3 concentrations are able to overcome the Ca-dependent inhibition of channel activity, apparently due to a low affinity InsP3 binding site (Kaftan, E.J., B.E. Ehrlich, and J. Watras. 1997. J. Gen. Physiol. 110:529-538). Constants from binding analyses and channel activity determinations were used to develop a mathematical model that fits the complex Ca-dependent regulation of the type 1 InsP3-gated Ca channel. This model accurately simulated both steady state data (channel open probability and InsP3 binding) and kinetic data (channel activity and open time distributions), and yielded testable predictions with regard to the regulation of this intracellular Ca channel. Information gained from these analyses, and our current molecular model of this Ca channel, will be important for understanding the basis and regulation of intracellular Ca waves and oscillations in intact cells.

Calcium signaling molecules in human cerebellum at midgestation and in ataxia.

A fundamental question in brain development is how neurons make the precise topographic connections necessary for function. The hypothesis that transient expression of calcium (Ca2+) signaling molecules may have a role in this process was tested by studying human cerebella at midgestation. In addition, four adult brains, two controls and two from patients with ataxia, were studied as well. The temporal and spatial distribution of intracellular Ca2+ channel/receptors, inositol trisphosphate receptor type 1 (IP3R1) and ryanodine receptor (RyR) and three Ca2+ binding proteins were examined with immunocytochemical methods. A positive immune reaction with all markers of Ca2+ signaling was found in the Purkinje cell layer starting from 17 g.w. (gestational weeks), the youngest age studied. The immune reactions were not homogeneous throughout the extent of the Purkinje cell layer, but instead displayed a 'patchy' appearance in all intrauterine stages. In the adult cerebellum the expression of Ca2+ signaling molecules was homogenous. In the two cerebella obtained from patients suffering from ataxia, a several-fold reduction of immunostaining with IP3R1 was found. Our findings suggest that transient and differential mobilization of intracellular Ca2+ in seemingly homogenous neuronal types may play a role in development of highly organized projection maps of the cerebellar cortex. Moreover, lack of IP3R1 in the diseased brains suggests that internal stores of Ca2+ play an important role in normal function of the cerebellum.

Type III InsP3 receptor channel stays open in the presence of increased calcium.

The inositol 1,4,5-trisphosphate receptor (InsP3R) is the main calcium(Ca2+) release channel in most tissues. Three isoforms have been identified, but only types I and II InsP3R have been characterized. Here we examine the functional properties of the type III InsP3R because this receptor is restricted to the trigger zone from which Ca2+ waves originate and it has distinctive InsP3-binding properties. We find that type III InsP3R forms Ca2+ channels with single-channel currents that are similar to those of type I InsP3R; however, the open probability of type III InsP3R isoform increases monotonically with increased cytoplasmic Ca2+ concentration, whereas the type I isoform has a bell-shaped dependence on cytoplasmic Ca2+. The properties of type III InsP3R provide positive feedback as Ca2+ is released; the lack of negative feedback allows complete Ca2+ release from intracellular stores. Thus, activation of type III InsP3R in cells that express only this isoform results in a single transient, but global, increase in the concentration of cytosolic Ca2+. The bell-shaped Ca2+-dependence curve of type I InsP3R is ideal for supporting Ca2+ oscillations, whereas the properties of type III InsP3R are better suited to signal initiation.

Characterization of the ryanodine receptor/channel of invertebrate muscle.

Electron-microscopic analysis was used to show that invertebrate muscle has feetlike structures on the sarcoplasmic reticulum (SR) displaying the typical four-subunit appearance of the calcium (Ca2+) release channel/ryanodine receptor (RyR) observed in vertebrate skeletal muscle (K. E. Loesser, L. Castellani, and C. Franzini-Armstrong. J. Muscle Res. Cell Motil. 13: 161-173, 1992). SR vesicles from invertebrate muscle exhibited specific ryanodine binding and single channel currents that were activated by Ca2+, caffeine, and ATP and inhibited by ruthenium red. The single channel conductance of this invertebrate RyR was lower than that of the vertebrate RyR (49 and 102 pS, respectively). Activation of lobster and scallop SR Ca2+ release channel, in response to cytoplasmic Ca2+ (1 nM-10 mM), reflected a bell-shaped curve, as is found with the mammalian RyR. In contrast to a previous report (J.-H. Seok, L. Xu, N. R. Kramarcy, R. Sealock, and G. Meissner, J. Biol. Chem. 267: 15893-15901, 1992), our results show that regulation of the invertebrate and vertebrate RyRs is quite similar and suggest remarkably similar paths in these diverse organisms.