Modelling pulse wave propagation in the rabbit systemic circulation to assess the effects of altered nitric oxide synthesis

Pulse wave propagation in the mature rabbit systemic circulation was simulated using the one-dimensional equations of blood flow in compliant vessels. A corrosion cast of the rabbit circulation was manufactured to obtain arterial lengths and diameters. Pulse wave speeds and inflow and outflow boundary conditions were derived from in vivo data. Numerical results captured the main features of in vivo pressure and velocity pulse waveforms in the aorta, brachiocephalic artery and central ear artery. This model was used to elucidate haemodynamic mechanisms underlying changes in peripheral pulse waveforms observed in vivo after administering drugs that alter nitric oxide synthesis in the endothelial cells lining blood vessels. According to our model, these changes can be explained by single or combined alterations of blood viscosity, peripheral resistance and compliance, and the elasticity of conduit arteries.     

Mechanism and energetics of proton translocation by the respiratory heme-copper oxidases

Recent time-resolved optical and electrometric experiments have provided a sequence of events for the proton-translocating mechanism of cytochrome c oxidase. These data also set limits for the mechanistic, kinetic, and thermodynamic parameters of the proton pump, which are analysed here in some detail. The analysis yields limit values for the pK of the “pump site”, its modulation during the proton-pumping process, and suggests its identity in the structure. Special emphasis is made on side-reactions that may short-circuit the pump, and the means by which these may be avoided. We will also discuss the most prominent proton pumping mechanisms proposed to date in relation to these data.     

The causes of reduced proton-pumping efficiency in type B and C respiratory heme-copper oxidases,and in some mutated variants of type A

The heme-copper oxidases may be divided into three categories, A, B, and C, which include cytochrome c and quinol-oxidising enzymes. All three types are known to be proton pumps and are found in prokaryotes, whereas eukaryotes only contain A-type cytochrome c oxidase in their inner mitochondrial membrane. However, the bacterial B- and C-type enzymes have often been reported to pump protons with an H⁺/e^- ratio of only one half of the unit stoichiometry in the A-type enzyme. We will show here that these observations are likely to be the result of difficulties with the measuring technique together with a higher sensitivity of the B- and C-type enzymes to the protonmotive force that opposes pumping. We find that under optimal conditions the H⁺/e^- ratio is close to unity in all the three heme-copper oxidase subfamilies. A higher tendency for proton leak in the B- and C-type enzymes may result from less efficient gating of a proton pump mechanism that we suggest evolved before the so-called D-channel of proton transfer. There is also a discrepancy between results using whole bacterial cells vs. phospholipid vesicles inlaid with oxidase with respect to the observed proton pumping after modification of the D-channel residue asparagine-139 (Rhodobacter sphaeroides numbering) to aspartate in A-type cytochrome c oxidase. This discrepancy might also be explained by a higher sensitivity of proton pumping to protonmotive force in the mutated variant. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.     

Multidrug Efflux Pump AcrAB of Salmonella typhimurium Excretes Only Those β-Lactam Antibiotics Containing Lipophilic Side Chains

We found that the previously reported SS-B drug-supersusceptible mutant of Salmonella typhimurium (S. Sukupolvi, M. Vaara, I. M. Helander, P. Viljanen, and P. H. Mäkelä, J. Bacteriol. 159:704–712, 1984) had a mutation in the acrAB operon. Comparison of this mutant with its parent strain and with an AcrAB-overproducing strain showed that the activity of the AcrAB efflux pump often produced significant resistance to β-lactam antibiotics in the complete absence of β-lactamase. The effect of AcrAB activity on resistance was more pronounced with agents containing more lipophilic side chains, suggesting that such compounds were better substrates for this pump. This correlation is consistent with the hypothesis that only those molecules that become at least partially partitioned into the lipid bilayer of the cytoplasmic membrane are captured by the AcrAB pump. According to this mechanism, the pump successfully excretes even those β-lactams that fail to traverse the cytoplasmic membrane, because these compounds are likely to become partitioned into the outer leaflet of the bilayer. Even the compounds with lipophilic side chains were shown to penetrate across the outer membrane relatively rapidly, if the pump was inactivated genetically or physiologically. The exclusion of such compounds, exemplified by nafcillin, from cells of the wild-type S. typhimurium was previously interpreted as the result of poor diffusion across the outer membrane (H. Nikaido, Biochim. Biophys. Acta 433:118–132, 1976), but it is now recognized as the consequence of efficient pumping out of entering antibiotics by the active efflux process.     

The pumping mechanism of the nematode esophagus

The radial orientation of the myofilaments in the nematode esophagus raises interesting questions as to how such a structure can function as a pump. A physical model of the esophagus of Ascaris lumbricoides was developed and the membrane theory of shells applied in order to relate the observed dimensional changes to myofilament force, pressure stresses, and membrane elastic constants. By stressing the excised esophagus passively with osmotic pressure, the esophagus was shown to be elastically anisotropic with the ratio of circumferential to longitudinal elastic constants, E_ψ/E_l 2.74. When this value was incorporated, the model predicted the ratio of the respective strains, ε_ψ/ε_l, to be 0.52 during an equilibrium contraction of the esophagus. This agreed with the experimental value, 0.46 ± 0.10, measured during occasional, prolonged muscle contractions. When measured during normal pumping, on the other hand, the value of ε_ψ/ε_l was 0 ± 0.10. This indicated that a nonequilibrium condition normally occurs in which a greater myofilament force per unit area of lumen membrane is not balanced by internal pressure and therefore acceleration of the lumen contents and negative intraluminal pressure occurs.

The pumping action of esophagi dissected from Ascaris was observed to be normally peristaltic and periodic. Contraction was initiated by a spontaneous depolarization that propagated at 4.0 ± 0.20 cm/s along the esophageal membrane. A wave of localized increases in the internal pressure of the muscle and localized changes in external dimensions was observed. A subsequent spontaneous repolarization, which propagated at 5.8 ± 0.23 cm/s, triggered relaxation of the muscle during which the localized pressure and dimensional changes returned to resting values. A mechanism was deduced in which fluid is drawn into and moved along the lumen by the wave of contraction. During the wave of relaxation, the lumen contents are pressurized and injected into the intestine by elastic restoring forces.

     

Fire-diffuse-fire calcium waves in confined intracellular spaces

The propagation of fire-diffuse-fire Ca²⁺ waves through a three-dimensional rectangular domain is considered. The domain is infinite in extent in the direction of propagation but with lateral barriers to diffusion which contain Ca²⁺ pumps. The Ca²⁺ concentration profile due to the firing of a release site (spark) is derived analytically based on the Green’s function for the diffusion equation on the domain. The existence, stability and speed of these waves is shown to be critically dependent on the dimensions of the domain and the Ca²⁺ pump rate. It is shown that the smaller the dimensions of the region, the lower the Ca²⁺ release flux required for wave propagation, and the higher the wave speed. Also it is shown that the region may support multiple Ca²⁺ wavefronts of varying wave speed. This model is relevant to subsarcolemmal waves in atrial myocytes (Kockskämper et al., 2001, Biophys. J. 81, 2590–2605), and the results may be of importance in understanding the roles of the endoplasmic/sarcoplasmic reticulum, surface membranes and Ca²⁺ pumps in the intracellular Ca²⁺ dynamics of cells.     

New perspectives on the evolution of lung ventilation mechanisms in vertebrates

In the traditional view of vertebrate lung ventilation mechanisms, air-breathing fishes and amphibians breathe with a buccal pump, and amniotes breathe with an aspiration pump. According to this view, no extant animal exhibits a mechanism that is intermediate between buccal pumping and aspiration breathing; all lung ventilation is produced either by expansion and compression of the mouth cavity via the associated cranial and hyobranchial musculature (buccal pump), or by expansion of the thorax via axial musculature (aspiration pump). However, recent work has shown that amphibians exhibit an intermediate mechanism, in which axial muscles are used for exhalation and a buccal pump is used for inhalation. These findings indicate that aspiration breathing evolved in two steps: first, from pure buccal pumping to the use of axial musculature for exhalation and a buccal pump for inspiration; and second, to full aspiration breathing, in which axial muscles are used for both inhalation and exhalation. Furthermore, the traditional view also holds that buccal pump breathing was lost shortly after aspiration breathing evolved. This view is now being challenged by the discovery that several species of lizards use a buccal pump to augment costal aspiration during exercise. This result, combined with the observation that a behavior known as “buccal oscillation” is found in all amniotes except for mammals, suggests that a reappraisal of the role of buccal pumping in extant and extinct amniotes is in order.Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Predictive Modeling of In Vivo Response to Gemcitabine in Pancreatic Cancer

A clear contradiction exists between cytotoxic in-vitro studies demonstrating effectiveness of Gemcitabine to curtail pancreatic cancer and in-vivo studies failing to show Gemcitabine as an effective treatment. The outcome of chemotherapy in metastatic stages, where surgery is no longer viable, shows a 5-year survival <5%. It is apparent that in-vitro experiments, no matter how well designed, may fail to adequately represent the complex in-vivo microenvironmental and phenotypic characteristics of the cancer, including cell proliferation and apoptosis. We evaluate in-vitro cytotoxic data as an indicator of in-vivo treatment success using a mathematical model of tumor growth based on a dimensionless formulation describing tumor biology. Inputs to the model are obtained under optimal drug exposure conditions in-vitro. The model incorporates heterogeneous cell proliferation and death caused by spatial diffusion gradients of oxygen/nutrients due to inefficient vascularization and abundant stroma, and thus is able to simulate the effect of the microenvironment as a barrier to effective nutrient and drug delivery. Analysis of the mathematical model indicates the pancreatic tumors to be mostly resistant to Gemcitabine treatment in-vivo. The model results are confirmed with experiments in live mice, which indicate uninhibited tumor proliferation and metastasis with Gemcitabine treatment. By extracting mathematical model parameter values for proliferation and death from monolayer in-vitro cytotoxicity experiments with pancreatic cancer cells, and simulating the effects of spatial diffusion, we use the model to predict the drug response in-vivo, beyond what would have been expected from sole consideration of the cancer intrinsic resistance. We conclude that this integrated experimental/computational approach may enhance understanding of pancreatic cancer behavior and its response to various chemotherapies, and, further, that such an approach could predict resistance based on pharmacokinetic measurements with the goal to maximize effective treatment strategies.     

Computational model for the transition from peristaltic to pulsatile flow in the embryonic heart tube

Early in development, the heart is a single muscle-wrapped tube without formed valves. Yet survival of the embryo depends on the ability of this tube to pump blood at steadily increasing rates and pressures. Developmental biologists historically have speculated that the heart tube pumps via a peristaltic mechanism, with a wave of contraction propagating from the inflow to the outflow end. Physiological measurements, however, have shown that the flow becomes pulsatile in character quite early in development, before the valves form. Here, we use a computational model for flow though the embryonic heart to explore the pumping mechanism. Results from the model show that endocardial cushions, which are valve primordia arising near the ends of the tube, induce a transition from peristaltic to pulsatile flow. Comparison of numerical results with published experimental data shows reasonably good agreement for various pressure and flow parameters. This study illustrates the interrelationship between form and function in the early embryonic heart.     

On the Mechanics of Cardiac Function of Drosophila Embryo

The heart is a vital organ that provides essential circulation throughout the body. Malfunction of cardiac pumping, thus, leads to serious and most of the times, to fatal diseases. Mechanics of cardiac pumping is a complex process, and many experimental and theoretical approaches have been undertaken to understand this process. We have taken advantage of the simplicity of the embryonic heart of an invertebrate, Drosophila melanogaster, to understand the fundamental mechanics of the beating heart. We applied a live imaging technique to the beating embryonic heart combined with analytical imaging tools to study the dynamic mechanics of the pumping. Furthermore, we have identified one mutant line that exhibits aberrant pumping mechanics. The Drosophila embryonic heart consists of only 104 cardiac cells forming a simple straight tube that can be easily accessed for real-time imaging. Therefore, combined with the wealth of available genetic tools, the embryonic Drosophila heart may serve as a powerful model system for studies of human heart diseases, such as arrhythmia and congenital heart diseases. We, furthermore, believe our mechanistic data provides important information that is useful for our further understanding of the design of biological structure and function and for engineering the pumps for medical uses.     

Determination of delay time in individual transfer function for central aortic pressure reconstruction

In previous research,time-delay(Δt)was a more important parameter than the reflection coefficient in the individual transfer function of central aortic pressure reconstruction.TheΔt can be obtained by electrocardiography(ECG)or phonocardiography(PCG).Because the pre-ejection period remains an uncertain factor,the present study used ECG and PCG to define the delay time and analyzed the accuracy of the reconstruction results.TheΔtpre is the actual delay time derived from the aorta to the carotid pressure wave,ΔtPCG is the time delay between the aortic valve component of the second heart sound and the dicrotic incisura of the carotid pressure wave,andΔtECG represents the delay from the interval of the ECG R-peak to the foot of the carotid pressure wave.Compared with the measured aortic pressure,the reconstruction result obtained byΔt=ΔtPCG slightly differed from the best result estimated byΔt=Δtpre.However,the differences between the result obtained byΔt=ΔtECG and the best result were significant in terms of the diastolic blood pressure,and pulse pressure,and especially in terms of the augmentation index and root-mean-square-error.Thus,theΔt should be determined by PCG for central aortic pressure reconstruction in practice.     

Validation of density–elasticity relationships for finite element modeling of human pelvic bone by modal analysis

In total hip arthroplasty and particularly in revision surgery, computer assisted pre-operative prediction of the best possible anchorage strategy for implant fixation would be a great help to the surgeon. Computer simulation relies on validated numerical models. In the current study, three density–elasticity relationships (No. 1–3) from the literature for inhomogeneous material parameter assignment from CT data in automated finite element (FE) modeling of long bones were evaluated for their suitability for FE modeling of human pelvic bone. Numerical modal analysis was conducted on 10 FE models of hemipelvic bone specimens and compared to the gold standard provided by experimental modal analysis results from a previous in-vitro study on the same specimens. Overall, calculated resonance frequencies came out lower than measured values. Magnitude of mean relative deviation of numerical resonance frequencies with regard to measured values is lowest for the density–elasticity relationship No. 3 (−15.9%) and considerably higher for both density–elasticity relationships No. 1 (−41.1%) and No. 2 (−45.0%). Mean MAC values over all specimens amount to 77.8% (No. 1), 78.5% (No. 2), and 83.0% (No. 3). MAC results show, that mode shapes are only slightly influenced by material distribution. Calculated resonance frequencies are generally lower than measured values, which indicates, that numerical models lack stiffness. Even when using the best suited (No. 3) out of three investigated density–elasticity relationships, in FE modeling of pelvic bone a considerable underestimation of model stiffness has to be taken into account.     

Computational models of heart pumping efficiencies based on contraction waves in spiral elastic bands

We present a framework for modeling biological pumping organs based on coupled spiral elastic band geometries and active wave-propagating excitation mechanisms. Two pumping mechanisms are considered in detail by way of example: one of a simple tube, which represents a embryonic fish heart and another more complicated structure with the potential to model the adult human heart. Through finite element modeling different elastic contractions are induced in the band. For each version the pumping efficiency is measured and the dynamics are evaluated. We show that by combining helical shapes of muscle bands with a contraction wave it is possible not only to achieve efficient pumping, but also to create desired dynamics of the structure. As a result we match the function of the model pumps and their dynamics to physiological observations.     

Imprinting analysis of the mouse chromosome 7C region in DNMT1-null embryos

The mouse chromosome 7C, orthologous to the human 15q11–q13 has an imprinted domain, where most of the genes are expressed only from the paternal allele. The imprinted domain contains paternally expressed genes, Snurf/Snrpn, Ndn, Magel2, Mkrn3, and Frat3, C/D-box small nucleolar RNAs (snoRNAs), and the maternally expressed gene, Ube3a. Imprinted expression in this large (approximately 3–4 Mb) domain is coordinated by a bipartite cis-acting imprinting center (IC), located upstream of the Snurf/Snrpn gene. The molecular mechanism how IC regulates gene expression of the whole domain remains partially understood. Here we analyzed the relationship between imprinted gene expression and DNA methylation in the mouse chromosome 7C using DNA methyltransferase 1 (DNMT1)-null mutant embryos carrying Dnmt1^ps alleles, which show global loss of DNA methylation and embryonic lethality. In the DNMT1-null embryos at embryonic day 9.5, the paternally expressed genes were biallelically expressed. Bisulfite DNA methylation analysis revealed loss of methylation on the maternal allele in the promoter regions of the genes. These results demonstrate that DNMT1 is necessary for monoallelic expression of the imprinted genes in the chromosome 7C domain, suggesting that DNA methylation in the secondary differentially methylated regions (DMRs), which are acquired during development serves primarily to control the imprinted expression from the maternal allele in the mouse chromosome 7C.     

Inhibitors of proton pumping: effect on passive proton transport

Reported inhibitors of the Characean plasmalemma proton pump were tested for their ability to inhibit the passive H⁺ conductance which develops in Chara corallina Klein ex Willd. at high pH. Diethylstilbestrol inhibits the proton pump and the passive H⁺ conductance with about the same time course, at concentrations that have no effect on cytoplasmic streaming. N-Ethylmaleimide, a sulfhydryl reagent which is small and relatively nonpolar, also inhibits both pumping and passive conductance of H⁺. However, it also inhibits cytoplasmic streaming with about the same time course, and therefore could not be considered a specific ATPase inhibitor. p-Chloromercuribenzene sulfonate (PCMBS), a sulfhydryl reagent which is large and charged and hence less able to penetrate the membrane, does not inhibit pumping or conductance at low concentration. At high concentration, PCMBS sometimes inhibits pumping without affecting H⁺ conductance, but since streaming is also inhibited, the effect on the pump cannot be said to be specific. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide, a water soluble carbodiimide, weakly inhibits both pump and conductance, apparently specifically.     

Effects of Blood Pressure and Sex on the Change of Wave Reflection: Evidence from Gaussian Fitting Method for Radial Artery Pressure Waveform

An early return of the reflected component in the arterial pulse has been recognized as an important indicator of cardiovascular risk. This study aimed to determine the effects of blood pressure and sex factor on the change of wave reflection using Gaussian fitting method. One hundred and ninety subjects were enrolled. They were classified into four blood pressure categories based on the systolic blood pressures (i.e., ≤110, 111–120, 121–130 and ≥131 mmHg). Each blood pressure category was also stratified for sex factor. Electrocardiogram (ECG) and radial artery pressure waveforms (RAPW) signals were recorded for each subject. Ten consecutive pulse episodes from the RAPW signal were extracted and normalized. Each normalized pulse episode was fitted by three Gaussian functions. Both the peak position and peak height of the first and second Gaussian functions, as well as the peak position interval and peak height ratio, were used as the evaluation indices of wave reflection. Two-way ANOVA results showed that with the increased blood pressure, the peak position of the second Gaussian significantly shorten (P<0.01), the peak height of the first Gaussian significantly decreased (P<0.01) and the peak height of the second Gaussian significantly increased (P<0.01), inducing the significantly decreased peak position interval and significantly increased peak height ratio (both P<0.01). Sex factor had no significant effect on all evaluation indices (all P>0.05). Moreover, the interaction between sex and blood pressure factors also had no significant effect on all evaluation indices (all P>0.05). These results showed that blood pressure has significant effect on the change of wave reflection when using the recently developed Gaussian fitting method, whereas sex has no significant effect. The results also suggested that the Gaussian fitting method could be used as a new approach for assessing the arterial wave reflection.     

Terpenoid emissions from heated needles of Pinus sylvestris and their potential influences on forest fires

It is assumed that terpenoids in biomass-derived fuels have important influences on forest fires due to their enormous flammability. The fires consuming terpenoid-rich fuels always burn violently and spread fast. But the mechanism how terpenoids influence occurrence and propagation of fires are little known. Some terpenoids are volatile organic compounds (VOC) as they are released from vegetation and litter in natural environment. Hence, they contribute to the characteristic composition of the ambient air. Many studies have reported terpenoid emissions in natural environment from different perspective. Nevertheless there are only a few studies concerning terpenoid emissions from heated fuels. The present study explored the differences in terpenoid emissions from needles of Pinus sylvestris var. mongolica under natural and heated conditions. Terpenoids were sampled on Tenax-TA and analyzed using Thermal Desorption– Gas Chromatography–Mass Spectrometry (TD–GC–MS). The results showed that the emission rate of terpenoid from P. sylvestris in natural environment was low (0.167 lg g^-1 h^-1 DW). However, terpenoid emissions dramatically increased at the temperature of 200 °C, with a major component, a-pinene. Within 15 min, the emission of terpenoids emitted by heated needles was up to 16.314 lg g^-1 DW for total and 10.321 lg g^-1 DW for a-pinene. These considerable emissions of terpenoids from heated needles will have great influences on occurrence and propagation of forest fires.     

Two explanations for the compliant running paradox: reduced work of bouncing viscera and increased stability in uneven terrain

Economy is a central principle for understanding animal locomotion. Yet, compared with theoretical predictions concerning economy, animals run with compliant legs that are energetically costly. Here, we address this apparent paradox, highlighting two factors that predict benefits for compliant gaits: (i) minimizing cost of work associated with bouncing viscera; and (ii) leg control for robust stability in uneven terrain. We show that consideration of the effects of bouncing viscera predicts an energetic optimum for relatively compliant legs. To compare stability in uneven terrain, we introduce the normalized maximum drop (NMD), a measure based on simple kinematics, which predicts that compliant legs allow negotiation of relatively larger terrain perturbations without failure. Our model also suggests an inherent trade-off in control of leg retraction velocity (ω) for stability: low ω allows higher NMD, reducing fall risk, whereas high ω minimizes peak forces with terrain drops, reducing injury risk. Optimization for one of these factors explicitly limits the other; however, compliant legs relax this trade-off, allowing greater stability by both measures. Our models suggest compromises in leg control for economy and stability that might explain why animals run with compliant legs.     

Pre‐steady‐state kinetics and solvent isotope effects support the “billiard‐type” transport mechanism in Na +‐translocating pyrophosphatase

Membrane‐bound pyrophosphatase (mPPase) found in microbes and plants is a membrane H⁺ pump that transports the H⁺ ion generated in coupled pyrophosphate hydrolysis out of the cytoplasm. Certain bacterial and archaeal mPPases can in parallel transport Na⁺ via a hypothetical “billiard‐type” mechanism, also involving the hydrolysis‐generated proton. Here, we present the functional evidence supporting this coupling mechanism. Rapid‐quench and pulse‐chase measurements with [³²P]pyrophosphate indicated that the chemical step (pyrophosphate hydrolysis) is rate‐limiting in mPPase catalysis and is preceded by a fast isomerization of the enzyme‐substrate complex. Na⁺, whose binding is a prerequisite for the hydrolysis step, is not required for substrate binding. Replacement of H₂O with D₂O decreased the rates of pyrophosphate hydrolysis by both Na⁺‐ and H⁺‐transporting bacterial mPPases, the effect being more significant than with a non‐transporting soluble pyrophosphatase. We also show that the Na⁺‐pumping mPPase of Thermotoga maritima resembles other dimeric mPPases in demonstrating negative kinetic cooperativity and the requirement for general acid catalysis. The findings point to a crucial role for the hydrolysis‐generated proton both in H⁺‐pumping and Na⁺‐pumping by mPPases.