Kinetics of ADP-induced Human Platelet Shape Change: Apparent Positive Cooperativity

The kinetics of ADP-induced human platelet shape change have been examined. Initial velocities of platelet shape change were estimated by two methods: 1) the slope of the initial decrease in light transmission through stirred, citrated platelet-rich plasma, and 2) direct examination of platelet morphologies by phase-contrast microscopy. In both cases, a value of the Hill coefficient, n, significantly greater than 1 is obtained (2.0 +/- 0.2 and 1.8 +/- 0.2, respectively). The observed elevated value of n is not due to a substantial fraction of the ADP being platelet bound, the presence of factors in the plasma, platelet heterogeneity, of the influence of the rate of platelet shape change reversion. Our observations suggest that ADP-induced platelet shape change may be a positive cooperative or threshold type response

Time and Force Dependence of the Rupture of Glycoprotein IIb-IIIa-Fibrinogen Bonds between Latex Spheres

AbstractWe studied the shear-induced breakup of doublets of aldehyde/sulfate (A/S) latex spheres covalently linked with purified platelet GPIIb-IIIa receptor, and cross-linked by fibrinogen. Flow cytometry with fluorescein isothiocyanate-fibrinogen showed than an average of 22,500 molecules of active GPIIb-IIIa were captured per sphere, with a mean Kd=56nM for fibrinogen binding. The spheres, suspended in buffered 19% Ficoll 400 containing 120 or 240pM fibrinogen, were subjected to Couette flow in a counter-rotating cone-plate rheoscope. Doublets, formed by two-body collisions at low shear rate (G=8s−1) for ≤15min, were subjected to shear stress from 0.6 to 2.9 Nm−2, their rotations recorded until they broke up or were lost to view. Although breakup was time dependent, occurring mostly in the first 2 rotations after the onset of shear, the percentage of doublets broken up after 10 rotations were almost independent of normal hydrodynamic force, Fn: at 240 pN, 15.6, 16.0, and 17.0% broke up in the force range 70–150 pN, 150–230 pN, and 230–310 pN. Unexpectedly, at both [fibrinogen], the initial rate of breakup was highest in the lowest force range, and computer simulation using a stochastic model of breakup was unable to simulate the time course of breakup. When pre-sheared at low G for >15min, no doublets broke up within 10 rotations at 70<Fn<310 pN; it required >3min shear (>1110 rotations) at Fn=210 pN for significant breakup to occur. Other published work has shown that binding of fibrinogen to GPIIb-IIIa immobilized on plane surfaces exhibits an initial fast reversible process with relative low affinity succeeded by transformation of GPIIb-IIIa to a stable high-affinity complex. We postulate that most doublet breakups observed within 10 rotations were from a population of young doublets having low numbers of bonds, by dissociation of the initial receptor complex relatively unresponsive to force. The remaining, older doublets with GPIIb-IIIa in the high-affinity complex were not broken up in the time or range of forces studied

Disturbing Times: Medieval Pasts, Reimagined Futures

From Kehinde Wiley to W.E.B. Du Bois, from Nubia to Cuba, Willie Doherty’s terror in ancient landscapes to the violence of institutional Neo-Gothic, Reagan’s AIDS policies to Beowulf fanfiction, this richly diverse volume brings together art historians and literature scholars to articulate a more inclusive, intersectional medieval studies. It will be of interest to students working on the diaspora and migration, white settler colonialism and pogroms, Indigenous studies and decolonial methodology, slavery, genocide, and culturecide. The authors confront the often disturbing legacies of medieval studies and its current failures to own up to those, and also analyze fascist, nationalist, colonialist, anti-Semitic, and other ideologies to which the medieval has been and is yoked, collectively formulating concrete ethical choices and aims for future research and teaching. In the face of rising global fascism and related ideological mobilizations, contemporary and past, and of cultural heritage and history as weapons of symbolic and physical oppression, this volume’s chapters on Byzantium, Medieval Nubia, Old English, Hebrew, Old French, Occitan, and American and European medievalisms examine how educational institutions, museums, universities, and individuals are shaped by ethics and various ideologies in research, collecting, and teaching

Synthetic approaches for accessing rare-earth analogues of UiO-66

Rare-earth (RE) analogues of UiO-66 with non-functionalised 1,4-benzenedicarboxylate linkers are synthesised for the first time, and a series of synthetic approaches is provided to troubleshoot the synthesis. RE-UiO-66 analogues are fully characterised, and demonstrate a high degree of crystallinity, high surface area and thermal stability, consistent with the UiO-66 archetype

Multi-Cellular Logistics of Collective Cell Migration

During development, the formation of biological networks (such as organs and neuronal networks) is controlled by multicellular transportation phenomena based on cell migration. In multi-cellular systems, cellular locomotion is restricted by physical interactions with other cells in a crowded space, similar to passengers pushing others out of their way on a packed train. The motion of individual cells is intrinsically stochastic and may be viewed as a type of random walk. However, this walk takes place in a noisy environment because the cell interacts with its randomly moving neighbors. Despite this randomness and complexity, development is highly orchestrated and precisely regulated, following genetic (and even epigenetic) blueprints. Although individual cell migration has long been studied, the manner in which stochasticity affects multi-cellular transportation within the precisely controlled process of development remains largely unknown. To explore the general principles underlying multicellular migration, we focus on the migration of neural crest cells, which migrate collectively and form streams. We introduce a mechanical model of multi-cellular migration. Simulations based on the model show that the migration mode depends on the relative strengths of the noise from migratory and non-migratory cells. Strong noise from migratory cells and weak noise from surrounding cells causes “collective migration,” whereas strong noise from non-migratory cells causes “dispersive migration.” Moreover, our theoretical analyses reveal that migratory cells attract each other over long distances, even without direct mechanical contacts. This effective interaction depends on the stochasticity of the migratory and non-migratory cells. On the basis of these findings, we propose that stochastic behavior at the single-cell level works effectively and precisely to achieve collective migration in multi-cellular systems

Requirements for Membrane Attack Complex Formation and Anaphylatoxins Binding to Collagen-Activated Platelets

The activation of complement during platelet activation is incompletely understood.We sought to explore the formation of C5b-9 and anaphylatoxins binding to collagen-activated platelets.C5b-9, anaphylatoxins C3a, C4a and C5a, and anaphylatoxin receptors C3aR1 and C5aR were measured by flow cytometry and/or confocal microscopy. Platelet microparticles were quantified by flow cytometry, and their C5b-9 content was determined by western blot analyses. In all experiments, sodium citrate was used for blood anticoagulation.C5b-9 rapidly formed on the platelet surface following activation with collagen, TRAP, ADP or A23187, but was surprisingly restricted to a subset of platelets (1 to 15%) independently of P-selectin or phosphatidylserine exposure. Following collagen activation, C5b-9-positive platelets in thrombi were found associated with collagen fibres. C5b-9 formation was obliterated by Mg(2+)-EGTA and significantly reduced by the thrombin inhibitor hirudin (-37%, p<0.05), but was unaffected by chondroitinase, compstatin, SCH79797 (PAR-1 inhibitor), or in the PRP of a MBL-deficient donor. Compstatin and Mg(2+)-EGTA, but not hirudin, SCH79797 or chondroitinase, inhibited the formation of collagen-induced microparticles (-71% and -44%, respectively, p<0.04). These microparticles contained greater amounts of C5b-9 compared with the other agonists. Platelet activation by collagen or convulxin resulted in the strong binding of anaphylatoxins and the exposure of receptors C3aR1 and C5aR (CD88) on their surface.C5b-9 formation on collagen-activated platelets is i) partially controlled by thrombin, ii) restricted to a subset of platelets, and iii) can occur without P-selectin expression or phosphatidylserine exposure. Activated platelets bind anaphylatoxins on their surface and express C3a and C5a receptors, which may contribute to the localization of inflammatory processes during thrombosis

Wall shear stress as measured in vivo: consequences for the design of the arterial system

Based upon theory, wall shear stress (WSS), an important determinant of endothelial function and gene expression, has been assumed to be constant along the arterial tree and the same in a particular artery across species. In vivo measurements of WSS, however, have shown that these assumptions are far from valid. In this survey we will discuss the assessment of WSS in the arterial system in vivo and present the results obtained in large arteries and arterioles. In vivo WSS can be estimated from wall shear rate, as derived from non-invasively recorded velocity profiles, and whole blood viscosity in large arteries and plasma viscosity in arterioles, avoiding theoretical assumptions. In large arteries velocity profiles can be recorded by means of a specially designed ultrasound system and in arterioles via optical techniques using fluorescent flow velocity tracers. It is shown that in humans mean WSS is substantially higher in the carotid artery (1.1–1.3 Pa) than in the brachial (0.4–0.5 Pa) and femoral (0.3–0.5 Pa) arteries. Also in animals mean WSS varies substantially along the arterial tree. Mean WSS in arterioles varies between about 1.0 and 5.0 Pa in the various studies and is dependent on the site of measurement in these vessels. Across species mean WSS in a particular artery decreases linearly with body mass, e.g., in the infra-renal aorta from 8.8 Pa in mice to 0.5 Pa in humans. The observation that mean WSS is far from constant along the arterial tree implies that Murray’s cube law on flow-diameter relations cannot be applied to the whole arterial system. Because blood flow velocity is not constant along the arterial tree either, a square law also does not hold. The exponent in the power law likely varies along the arterial system, probably from 2 in large arteries near the heart to 3 in arterioles. The in vivo findings also imply that in in vitro studies no average shear stress value can be taken to study effects on endothelial cells derived from different vascular areas or from the same artery in different species. The cells have to be studied under the shear stress conditions they are exposed to in real life