The role of mechanical pressure difference in the generation of membrane voltage under conditions of concentration polarization

The mechanical pressure difference across the bacterial cellulose membrane located in a horizontal plane causes asymmetry of voltage measured between electrodes immersed in KCl solutions symmetrically on both sides of the membrane. For all measurements, KCl solution with lower concentration was above the membrane. In configuration of the analyzed membrane system, the concentration boundary layers (CBLs) are created only by molecular diffusion. The voltages measured in the membrane system in concentration polarization conditions were compared with suitable voltages obtained from the model of diffusion through CBLs and ion transport through the membrane. An increase of difference of mechanical pressure across the membrane directed as a difference of osmotic pressure always causes a decrease of voltage between the electrodes in the membrane system. In turn, for mechanical pressure difference across the membrane directed in an opposite direction to the difference of osmotic pressure, a peak in the voltage as a function of mechanical pressure difference is observed. An increase of osmotic pressure difference across the membrane at the initial moment causes an increase of the maximal value of the observed peak and a shift of this peak position in the direction of higher values of the mechanical pressure differences across the membrane.     

Transport of water from concentrated to dilute solutions in cells of Nitella

The transport of water from concentrated to dilute solutions which occurs in the kidney and in a variety of living cells presents a problem of fundamental importance. If the cell acts as an osmometer we may expect to bring about such transport by creating an inwardly directed osmotic drive which is higher in one part of the cell than in other regions of the same cell. The osmotic drive is defined as the difference between internal and external osmotic pressure. Experiments with Nitella show that this expectation is justified. If water is placed at one end of the cell (A) and 0.4 M sucrose with an osmotic pressure of 11.2 atmospheres at the other end (B) water enters at A, passes along inside the cell, and escapes at B leaving behind at B the solutes which cannot pass out through the protoplasm. Hence the internal osmotic pressure becomes much higher at B than at A. When 0.4 M sucrose at B is replaced by 0.3 M sucrose with an osmotic pressure of 8.1 atmospheres we find that water enters at B, passes along inside the cell, and escapes at A so that water is transported from a concentrated to a dilute solution although the difference in osmotic pressure of the 2 solutions is more than 8 atmospheres. The solution at B thus becomes more concentrated. It is evident that if metabolism produces a higher osmotic pressure and consequently a higher inwardly directed osmotic drive in one region of the cell as compared with other parts of the same cell water may be transferred from a concentrated to a dilute solution so that the former solution becomes still more concentrated.     

Hydrostatic Pressure and Proteins: Basic Concepts and New Data

In this paper we review some basic facts about the reversible and irreversible effects of high pressure on proteins. The effects include changes in intra- or intermolecular interactions (noncovalent bonds), in conformation and in solvation. Particular attention is directed to the interpretation of data where pressure-temperature dependency is an important phenomenon. Using model reactions, we have formulated a putative interpretation of physiological problems; we use these to explain how biological systems maintain activity when the temperature decreases and pressure increases, as in the case of barophilic micro-organisms in the deep sea world.     

Posterior acceleration as a mechanism of blunt traumatic injury of the aorta

Rupture of the thoracic aorta is a leading cause of rapid fatality in automobile crashes, but the exact mechanisms of this injury remain unidentified. One commonly postulated mechanism is a differential motion of the aortic arch relative to the heart and its neighboring vessels caused by high-magnitude acceleration of the thorax. This paper investigates acceleration as an aortic injury mechanism using nine impact-sled tests with human cadaver thoraces. The test system utilized generates very high posteriorly directed thoracic accelerations with minimal compression of the chest. The sled tests resulted in peak mid-spine accelerations of 169+/-35.0 g (mean+/-standard deviation) with sustained mid-spine accelerations of up to 80 g for 20 ms in most cases. The tests resulted in maximum chest compressions of 7+/-3.1% of the total chest depth, and maximum recorded increases in intra-aortic, tracheal, and esophageal pressure of 177, 112, and 156 kPa, respectively. No macroscopic injuries to the thoracic aorta resulted from these tests, though other limited visceral injury was observed. The results suggest that posteriorly directed acceleration alone (up to the magnitudes studied here) is not sufficient to cause gross aortic injury. Furthermore, the observed transient increases in intra-aortic and extra-aortic pressure indicate that complex pressure distributions are present during dynamic thoracic deceleration events. This suggests that any attempt to model traumatic aortic injury should include consideration for both the intra-aortic fluid pressure and the extra-aortic, intra-thoracic pressure present during the event.     

Reye's Syndrome

Reye''s syndrome (encephalopathy with fatty infiltration of the viscera) is an acute illness of childhood that produces hepatic dysfunction and metabolic encephalopathy. The disease is fatal in as many as 40% of cases. The cause is unknown. Several environmental agents, particularly salicylates and aflatoxin, have been implicated as possible toxins in this disorder. Treatment is directed at controlling intracranial pressure, reversing metabolic abnormalities and providing intensive supportive care. Normal neurologic function returns in most survivors.     

Pressure profile along the microvascular network and its control

The distribution of pressures within the arcading microvessels in numerous tissues is described and evaluated relative to potential sites for the control of blood flow and/or pressure. In various tissues a large fraction of the total systemic pressure is dissipated by small arteries and/or large arterioles and by small arterioles, the classical high-resistance vessels. Thus, these sites must be linked to the regulation and distribution of blood flow and pressure within the network as evidenced by the shifts in the profiles of pressures in these vessels after vasoactive stimuli. In fact, there may be some coupling of vasoactivity between these areas of vascular resistance. The vasodilator activity may predominate in small arterioles whereas the neural control may be directed to the small arteries and large arterioles. Thus, physiological, pharmacological, and pathological influences may affect the control of blood flow and/or pressure at one or both of these sites.     

Watch Your Tone: Social Conditions Modulate Singing Strategies

Bird song is typically depicted as a male singing a long‐distance signal to potentially unknown receivers to (1) deter males and (2) attract females. Nevertheless, many songbirds sing from close distances to a known receiver; males of these species may be under more intense selective pressure to modify their songs depending on the sex of the receiver in order to convey different motivational states (aggression versus courtship) to the different sexes. In a laboratory setting, we examined how receiver sex affected within‐song variation of the close‐range singing behavior in the brown‐headed cowbird (Molothrus ater). Although we know that cowbird song is influenced by flock composition, it is still unclear as to how the cowbird modifies his song based on social context. Using a cross‐correlation analysis of each male's different song types, we found that pairs of songs were significantly more dissimilar if they were directed to females compared with songs directed to males. We subsequently tested whether there were any consistent spectral or temporal patterns in the songs males gave to females versus to males. Our results lend support for the Motivational Structural Rules Hypothesis as songs directed toward males had higher entropy (i.e., harshness) than the same song type directed toward females. Our results suggest that cowbirds may have evolved the ability to alter multiple dimensions of their singing behavior based on receiver sex.     

Flow through a Collapsible Tube: Experimental Analysis and Mathematical Model

Flow through thin-wall axisymmetric tubes has long been of interest to physiologists. Analysis is complicated by the fact that such tubes will collapse when the transmural pressure (internal minus external pressure) is near zero. Because of the absence of any body of related knowledge in other sciences or engineering, previous workers have directed their efforts towards experimental studies of flow in collapsible tubes. More recently, some attention has been given towards analytical studies. Results of an extensive series of experiments show that the significant system parameter is transmural pressure. The cross-sectional area of the tube depends upon the transmural pressure, and changes in cross-section in turn affect the flow geometry. Based on experimental studies, a lumped parameter system model is proposed for the collapsible tube. The mathematical model is simulated on a hybrid computer. Experimental data were used to define the functional relationship between cross-sectional area and transmural pressure as well as the relation between the energy loss coefficient and cross-sectional area. Computer results confirm the validity of the model for both steady and transient flow conditions.     

Formation of transversely oriented myofibrils in myocardiocytes in the presence of heart enlargement]

Myocardial hypertrophy was induced in rats and mice by training in the pressure chamber (high altitude hypoxia) or ligation of the apex of the heart. Transversely oriented myofibrils developed in the subsarcolemma area of some cardiomyocytes of the ventricles in a fortnight; the Z bands of the newly-formed myofibrils were connected with the T tubules as in the normal myofibrils. It is supposed that this phenomenon was due to the appearance under the sarcolemma of transversely directed mechanical forrces as a result of enlargement of the cell volume.     

The effect of the external medium on the gravity-induced polarity of cytoplasmic streaming in Chara corallina (Characeae)

Gravity induces a polarity of cytoplasmic streaming in vertical internodal cells of Chara such that the downwardly directed stream moves faster than the upwardly directed stream. In order to determine whether the statolith theory (in which intracellular sedimenting particles are responsible for gravity sensing) or the gravitational pressure theory (in which the entire protoplast acts as the gravity sensor) best explain the gravity response in Chara internodal cells, we controlled the physical properties of the external medium, including density and osmolarity, with impermeant solutes and examined the effect on the polarity of cytoplasmic streaming. As the density of the external medium is increased, the polarity of cytoplasmic streaming decreases and finally disappears when the density of the external medium is equal to that of the cell (1015 kg/m3). A further increase in the density of the external medium causes a reversal of the gravity response. These results are consistent with the gravitational pressure theory of gravity sensing since the buoyancy of the protoplast is dependent on the difference between the density of the protoplast and the external medium, and are inconsistent with the statolith theory since the buoyancy of intracellular particles are unaffected by changes in the external medium.     

利用雨生红球藻表达系统高通量筛选活力提高的阿特拉津氯水解酶突变子

阿特拉津氯水解酶定向改造的关键是开发一种廉价的、表型改变明显的高通量筛选方法。利用高错误倾向PCR和DNA洗牌相结合的突变方法,对来源于假单胞菌ADP和节杆菌AD1的阿特拉津氯水解酶基因进行随机突变,以雨生红球藻为受体、以阿特拉津为选择压力对突变文库进行高通量筛选。筛选到的12个突变子序列分析显示,突变均为点替换,位点分散在全基因上,是在高错误倾向PCR及DNA洗牌过程中逐渐累积形成的。酶活力分析显示,突变子的酶活力均高于野生株,在添加1.0 mg/L阿特拉津培养液中的活力是野生株的1.9~3.6倍,在添     

Laboratory-Directed Protein Evolution

Systematic approaches to directed evolution of proteins have been documented since the 1970s. The ability to recruit new protein functions arises from the considerable substrate ambiguity of many proteins. The substrate ambiguity of a protein can be interpreted as the evolutionary potential that allows a protein to acquire new specificities through mutation or to regain function via mutations that differ from the original protein sequence. All organisms have evolutionarily exploited this substrate ambiguity. When exploited in a laboratory under controlled mutagenesis and selection, it enables a protein to “evolve” in desired directions. One of the most effective strategies in directed protein evolution is to gradually accumulate mutations, either sequentially or by recombination, while applying selective pressure. This is typically achieved by the generation of libraries of mutants followed by efficient screening of these libraries for targeted functions and subsequent repetition of the process using improved mutants from the previous screening. Here we review some of the successful strategies in creating protein diversity and the more recent progress in directed protein evolution in a wide range of scientific disciplines and its impacts in chemical, pharmaceutical, and agricultural sciences.     

Change in the system of wing venation of Drosophila melanogaster under heat shock and selection

A change in the system of wing venation of Drosophila melanogaster appeared in response to heat shock and positive selection pressure directed to restoring the normal formation of wing radial vein, L2, that had been violated earlier by the recessive mutation of radius incompletes. Positive selection was effective, L2 having been formed correctly and completely to 35 generation. Besides, (+)-selection was accompanied by appearance of a small fragment of an additional vein at the wing tip. Selection directed to increase of size of this fragment resulted in the sufficient changes in the system of wing venation as a whole. It is suggested that, during evolution, transformation of wing venation of Drosophila was effected by the change of the way of prepattern realization, whereas the cells of wing plate continued to allow the formation of veins practically over a whole area.     

Recent advances in maximum entropy biasing techniques for molecular dynamics

ABSTRACT

This review describes recent advances by the authors and others on the topic of incorporating experimental data into molecular simulations through maximum entropy methods. Methods which incorporate experimental data improve accuracy in molecular simulation by minimally modifying the thermodynamic ensemble. This is especially important where force fields are approximate, such as when employing coarse-grain models, or where high accuracy is required, such as when attempting to mimic a multiscale self-assembly process. The authors review here the experiment directed simulation (EDS) and experiment directed metadynamics (EDM) methods that allow matching averages and distributions in simulations, respectively. Important system-specific considerations are discussed such as using enhanced sampling simultaneously, the role of pressure, treating uncertainty, and implementations of these methods. Recent examples of EDS and EDM are reviewed including applications to ab initio molecular dynamics of water, incorporating environmental fluctuations inside of a macromolecular protein complex, improving RNA force fields, and the combination of enhanced sampling with minimal biasing to model peptides     

Similarity between a kininogenase (kallikrein) from human large intestine and human urinary kallikrein.

A human colon kininogenase (kallikrein) was isolated by gel filtration on Sephacryl S-200 and affinity chromatography on Trasylolbound Sepharose, yielding a material with a specific activity of 1.3 U/mg (substrate: AcPheArgOEt). The molecular weight of the enzyme as estimated by gel filtration is approximately 70 000. After reduction with mercaptoethanol two bands were obtained in dodecyl sulfate eletrophoresis with molecular weights of 27 000 and 70 000. The bimolecular velocity constant for the inhibition by diisopropyl fluorophosphate was determined as 4 l x mol-1 x min-1. The preparation was characterized by immunological and enzymatic methods. Using the radioimmumoassay for human urinary kallikrein cross-reactivity and parallel binding curves were obtained. Kinin liberation from human high Mr-kininogen was totally inhibited by antibodies directed against human urinary kallikrein. Trasylol and diisopropyl fluorophosphate, but not by antibodies directed against human trypsin and plasma kallikrein. The effect on dog blood pressure was comparable to that obtained with human urinary kallikrein. The amino acid composition of human large intestine kallikrein is very similar to that of human urinary kallikrein.     

Neurotensin-like immunoreactivity generated by pepsin from human plasma and gastric tissue

The present study demonstrates precursors of neurotensin-like immunoreactivity (NTLI) endogenous to human gastric tissue and plasma, and the existence of a gastric NTLI-generating enzyme system. The molecular size of the NTLI-precursors in plasma and gastric tissue were estimated by gel permeation chromatography to be ca 50,000-60,000 and 60,000-70,000 Da, respectively. The neurotensin-like peptide generated from the precursor was detected with a carboxyl-terminally directed antiserum but did not cross-react with an amino-terminally directed antiserum. A neurotensin-like peptide isolated from pepsin-treated human plasma was characterized by mass spectrometry and its amino acid sequence determined. This novel nonapeptide, referred to as kinetensin, failed to affect pentagastrin-stimulated acid secretion or blood pressure in the rat. Sequence homologies between neurotensin, kinetensin and proteins of the serum albumin family suggest a common evolutionary origin and raise questions regarding albumin-like proteins as precursors of regulatory peptides.     

Cloning of the fliI gene from Rhodobacter sphaeroides WS8 by analysis of a transposon mutant with impaired motility

Abstract The formation of plaques by A phage in Escherichia coli was prevented by elevated hydrostatic pressure; phage plaques were not detected at 30 MPa. Furthermore, using promoter fragments derived from the malB operon, we showed that gene expression initiated from both promoters ( malK-lamB and malEFG ) was repressed by elevated hydrostatic pressure. Our findings suggest that high pressure affects gene expression directed by the malB regulatory interval, and this may cause a decrease in the quantities of A receptor protein, LamB.     

Genetic analysis of various behavioral and physiologic characteristics in hybrids between hypertensive and normotensive rats. Analysis of correlational connections]

Hereditary links between different behavioral and physiological traits were studied in rat strains SHR, WKY and their hybrids F1 and F2 by analysis of correlations in segregating and nonsegregating gene-rations. Genetic correlation of arterial pressure with body mass, intake of KC1 solution and the ability to avoidance learning (directed positively) and with characteristics of exploratory activity (directed negatively) was shown. These traits seemed to be possible genetic markers of arterial hypertension. Genetical correlates of the ability to elaborate active avoidance conditional reaction (arterial pressure and pain sensitivity) testify to relief of active avoidance learning in animals with inherited active-defensive type of behaviour, manifested by predisposition to pressor reactions and by suppressed emotional reactions to pain stimulation. Frequency in intertrial crossings during avoidance training displays positive correlation with characteristics of exploratory behaviour. Positive correlation between different characteristics of exploratory activity was established both in segregating and nonsegregating generations.     

Hypotensive properties of antibodies directed against an endogenous pressor peptide isolated from rat blood

Hypertensive factor (HF), a compound isolated from the erythrocytes of rats and tentatively identified as a peptide, has been shown to influence tissue calcium metabolism and induce prolonged blood pressure elevation. In the present study, we investigated the biological properties of antibodies directed against this peptide. Partially purified antibody preparations significantly decreased HF stimulation of lanthanum-resistant calcium uptake in rat aortic tissue in vitro. Infusion of the antibody preparation into spontaneously hypertensive (SH) or normotensive Sprague-Dawley rats resulted in a rapid decline in mean blood pressure of 54 and 34 Torr (1 Torr = 133.332 Pa), respectively. In contrast, infusion of the serum immunoglobulin preparations from controls (unimmunized and ovalbumin-immunized rabbits) had no significant effect on the blood pressure of SH or normotensive rats. The systolic blood pressure of SH rats was reduced for at least 72 h following a single injection of the antibody preparations, whereas the blood pressure of normotensive rats had returned to normal levels within 24 h following antibody injection. The results indicate that the anti-HF antibody preparation antagonizes the stimulation of calcium uptake by the peptide and acutely lowers blood pressure in SH and normotensive rats.