Subunit stoichiometry of a core conduction element in a cloned epithelial amiloride-sensitive Na+ channel

The molecular composition of a core conduction element formed by the alpha-subunit of cloned epithelial Na+ channels (ENaC) was studied in planar lipid bilayers. Two pairs of in vitro translated proteins were employed in combinatorial experiments: 1) wild-type (WT) and an N-terminally truncated alphaDeltaN-rENaC that displays accelerated kinetics (tauo = 32 +/- 13 ms, tauc = 42 +/- 11 ms), as compared with the WT channel (tauc1 = 18 +/- 8 ms, tauc2 = 252 +/- 31 ms, and tauo = 157 +/- 43 ms); and 2) WT and an amiloride binding mutant, alphaDelta278-283-rENaC. The channels that formed in a alphaWT:alphaDeltaN mixture fell into two groups: one with tauo and tauc that corresponded to those exhibited by the alphaDeltaN-rENaC alone, and another with a double-exponentially distributed closed time and a single-exponentially distributed open time that corresponded to the alphaWT-rENaC alone. Five channel subtypes with distinct sensitivities to amiloride were found in a 1alphaWT:1alphaDelta278-283 protein mixture. Statistical analyses of the distributions of channel phenotypes observed for either set of the WT:mutant combinations suggest a tetrameric organization of alpha-subunits as a minimal model for the core conduction element in ENaCs.     

A parallel Monte Carlo search algorithm for the conformational analysis of polypeptides

In recent years several approaches have been proposed to overcome the multiple-minima problem associated with nonlinear optimization techniques used in the analysis of molecular conformations. One such technique based on a parallel Monte Carlo search algorithm is analyzed. Experiments on the Intel iPSC/2 confirm that the attainable parallelism is limited by the underlying acceptance rate in the Monte Carlo search. It is proposed that optimal performance can be achieved in combination with vector processing. Tests on both the IBM 3090 and Intel iPSC/2-VX indicate that vector performance is related to molecule size and vector pipeline latency.     

A constant-time dynamic storage allocator for real-time systems

Dynamic memory allocation has been used for decades. However, it has seldom been used in real-time systems since the worst case of spatial and temporal requirements for allocation and deallocation operations is either unbounded or bounded but with a very large bound. In this paper, a new allocator called TLSF (Two Level Segregated Fit) is presented. TLSF is designed and implemented to accommodate real-time constraints. The proposed allocator exhibits time-bounded behaviour, O(1), and maintains a very good execution time. This paper describes in detail the data structures and functions provided by TLSF. We also compare TLSF with a representative set of allocators regarding their temporal cost and fragmentation. Although the paper is mainly focused on timing analysis, a brief study and comparative analysis of fragmentation incurred by the allocators has been also included in order to provide a global view of the behaviour of the allocators. The temporal and spatial results showed that TLSF is also a fast allocator and produces a fragmentation close to that caused by the best existing allocators.

A Task Model to Reduce Control Delays

Industrial control applications are usually developed in two phases: control design and real-time system implementation. In the control design stage a regulator is obtained and later it is translated into an algorithm in the implementation phase. Traditionally, these two phases have been developed in separate ways. Recently, some works have pointed out the necessity of the integration of the control design and its implementation. One of these works reduce the delay variance of control tasks (defined as the control action interval (CAI) and data acquisition interval (DAI) parameters) splitting every task into three parts. The CAI reduction method highly reduces the delay variance and improves the control performance. This work shows how to evaluate these delays under static and dynamic scheduling policies. A new task model is proposed in order to reduce the CAI and DAI parameters, which implies an improvement in the control performance. The new task model will be implemented in a real process, and the experimental measurements will show how, effectively, the control performance is highly improved with the methods presented in this paper.     

Influence of the type of forage supplied to ewes in pre- and post-partum periods on the meat fatty acids of suckling lambs

The aim of this study was to evaluate the use of forage diets (grazing vs. hay) around the time of ewe parturition, on the fatty acids profile of suckling lamb meat (10-12 kg body weight). Forty-eight multiparous single-bearing ewes were used. The experimental treatments were conducted during the last 5 weeks of pregnancy and the 5 weeks of lactation in a 2 × 2 factorial design. Ewes were fed ad libitum on pastures or hay in the autumn. Results showed that milk from grazing ewes during the pre-partum period had a higher content of PUFA and CLA (P < 0.05) and VA, CLA in their suckling lambs' meat (P < 0.05). The effect in post-partum feeding was greater, revealing higher CLA, PUFA/SFA, PUFA n-3 and PUFA n-6/n-3 in milk and meat (P < 0.05). The CLA, VA and PUFA n-6/n-3 ratios are those that are most affected by grazing. Pre-partum grazing, regardless of post-partum feeding, improves FA composition, increasing CLA content in both milk and meat.     

Enhanced Sliding Wear Resistance of Technical Alloys by Hard Particle Reinforcement Using Machine Hammer Peening

Machine hammer peening is a surface treatment technique originally developed for smoothening tools and mold surfaces. Treated surfaces are locally cold-worked, which results in a hardness increase and the induction of compressive residual stresses. In the present work, the feasibility of using this technique as a tool for embedding tungsten carbide hard particles on engineering-relevant substrate materials is systematically investigated. Tungsten carbide particles of three different sizes were embedded onto selected substrates using machine hammer peening. The particle embedment quality of the engineered surfaces was evaluated and correlated to the substrates' mechanical properties. The resulting tribological performance was investigated under reciprocating sliding conditions and the dominant wear mechanisms were correlated with the diameter of the embedded particles. The results show that machine hammer peening is a suitable technique for embedding hard particles in substrates of various materials, which additionally results in an enhancement in wear resistance, thus opening up a wide range of potential applications in tribologically loaded surfaces.     

Primary epiploic appendagitis: US and CT findings

A retrospective review is presented of seven cases of epiploic appendagitis, with surgical confirmation in one case. The main clinico-analytical data and the US and CT findings are described, as well as the histopathologic features in the sole case that underwent surgical resection. We also calculated the frequency of this entity in patients undergoing emergency abdominal US on clinical suspicion of diverticulitis. In all seven cases the clinico-analytical evidence was nonspecific (localized acute abdominal pain and slight leukocytosis), mimicking in six cases the clinical presentation of sigmoid diverticulitis and in one case that of acute appendicitis. US imaging findings were characteristic: a hyperechoic mass localized under the point of maximum pain, adjacent to the anterior peritoneal wall and fixed during deep breathing. In none of the cases did color Doppler US show flow. CT findings were also typical and showed a mass with a peripheral hyperattenuated rim surrounding an area of fatty attenuation. Overall 7.1 % of patients investigated to exclude sigmoid diverticulitis finally showed findings of primary epiploic appendagitis. Primary epiploic appendagitis thus shows characteristic US and CT findings that allow its diagnosis and follow-up. This entity is much more frequent than previously reported, especially in patients referred for US to exclude sigmoid diverticulitis.     

Intracellular diadenosine polyphosphates: a novel second messenger in stimulus-secretion coupling

In pancreatic beta-cells, stimulatory glucose concentrations increase cytosolic diadenosine polyphosphates ([ApnA]i) to concentrations sufficient to block ATP-sensitive K+ (KATP) channels. High-performance liquid chromatography and patch clamp techniques were used to study the metabolic pathways by which pancreatic beta-cells synthesize ApnA and the mechanism through which ApnA inhibit KATP channels. ApnA show a glucose- and time-dependent cytosolic concentration increase parallel, though 30- to 50-fold higher, to changes observed in adenine nucleotides. Other fuel secretagogues, leucine and 2-ketoisocaproate, raise [ApnA]i as efficiently as 22 mM glucose. Blockade of glycolysis or Krebs cycle decreases glucose-induced [ApnA]i. No significant increase in cytosolic ApnA concentrations is induced by nonnutrient secretagogues or nonmetabolizable nutrient secretagogues. Inorganic pyrophosphatase inhibition with sodium fluoride blocks 22 mM glucose-induced [ApnA]i increase. ApnA inhibition of KATP channel resembles that of ATP in efficacy, but shows clear functional differences. Unlike ATP, Ap4A does not restore channel activity after rundown. Furthermore, these compounds do not compete with each other for the same site. These features suggest a prominent role for Ap4A in beta-cell function, comparable to ATP. We conclude that nutrient metabolism through pyrophosphatase activation is necessary to induce ApnA synthesis, which in turn constitutes a new, ATP-independent, metabolic regulator of KATP channel activity.     

Anticholinergic effects of strychnine in the cochlea do not involve muscarinic receptors

Central control of cochlear function is mediated by the cholinergic (medial) efferent system and both muscarinic and nicotinic acetylcholine receptors are thought to be present on outer hair cells. All the physiological effects of acetylcholine in the cochlea are blocked by strychnine and we therefore investigated whether strychnine interacts with muscarinic receptors in the cochlea. The effects of strychnine on both (3H)-quinuclidinyl benzylate binding and atropine sensitive carbachol-induced (3H)-inositol phosphate formation were examined. Strychnine (1 to 50 microM) has no effect on either quinuclidinyl benzylate binding or carbachol (1 mM)-induced inositol phosphate synthesis. Moreover, strychnine does not change basal inositol phosphate metabolism. These data indicate that muscarinic receptors are not sensitive to strychnine at concentrations which are known to block the effects of acetylcholine on outer hair cells.