The influence of skeletal muscle cell volume on the regulation of carbohydrate uptake and muscle metabolism

This study investigated the regulation of carbohydrate metabolism and glucose uptake through changes in skeletal muscle cell volume. Using an established invitro isolated whole muscle model, soleus (SOL) and extensor digitorum longus (EDL) muscles were dissected from male rats and incubated in an organ bath containing Sigma medium-199 with 8 mM D-glucose altered to target osmolality (hypo-osmotic: HYPO, iso-osmotic: ISO, hyper-osmotic: HYPER; 190, 290, 400 mmol/kg). Muscles were divided into two groups; metabolite (MM) and uptake (MU). MM (N=48) were incubated for 60 minutes and were then immediately flash frozen. MU (N=24) were incubated for 30 minutes and then the extracellular fluid was exchanged for media containing ^H-glucose and ^'*C-mannitol and incubated for another 30 minutes. After the incubation, the muscles were freeze clamped. Results demonstrated a relative water decrease and increase in HYPER and HYPO, respectively. EDL and SOL glucose uptakes were found to be significantly greater in HYPER conditions. The HYPER condition resulted in significant alterations in muscle metabolite concentrations (lower glycogen, elevated lactate, and G-6-P) suggesting a catabolic cell state, and an increase in glycogen synthase transformation when compared to the HYPO group. In conclusion, skeletal muscle cell volume alters rates of glucose uptake with further alterations in muscle metabolites and glycogen synthase transformation.

Diffusion Monte Carlo study of electronic properties for H and Be atoms /

We examined three different algorithms used in diffusion Monte Carlo (DMC) to study their precisions and accuracies in predicting properties of isolated atoms, which are H atom ground state, Be atom ground state and H atom first excited state. All three algorithms — basic DMC, minimal stochastic reconfiguration DMC, and pure DMC, each with future-walking, are successfully impletmented in ground state energy and simple moments calculations with satisfactory results. Pure diffusion Monte Carlo with future-walking algorithm is proven to be the simplest approach with the least variance. Polarizabilities for Be atom ground state and H atom first excited state are not satisfactorily estimated in the infinitesimal differentiation approach. Likewise, an approach using the finite field approximation with an unperturbed wavefunction for the latter system also fails. However, accurate estimations for the a-polarizabilities are obtained by using wavefunctions that come from the time-independent perturbation theory. This suggests the flaw in our approach to polarizability estimation for these difficult cases rests with our having assumed the trial function is unaffected by infinitesimal perturbations in the Hamiltonian.

Glucose dynamics in rat skeletal muscle : recovery from osmotic stress

The purpose of this study was to examine cell glucose kinetics in rat skeletal muscle during iso-osmotic recovery from hyper- and hypo-osmotic stress. Rat EDL muscles were incubated for sixty minutes in either HYPO (190 mmol/kg), ISO (290 mmol/kg), or HYPER (400 mmol/kg) media (Sigma medium-199, 8 mM glucose) according to an established in vitro whole muscle model. In addition to sixty minute baseline measures in aniso-osmotic conditions, (HYPO-0 n=8; ISO- 0, n=S; HYPER-0, n=8), muscles were subjected to either one minute (HYPO-1 n=8; ISO-1, n=8; HYPER-1, n=8) or five minutes (HYPO-5 n=8; ISO-5, n=8; HYPER-5, n=8) of iso-osmotic recovery media and analyzed for metabolite content and glycogen synthase percent activation. To determine glucose uptake during iso-osmotic recovery, muscles (n=6 per group) were incubated for sixty minutes in either hypo-, iso-, or hyper-osmotic media immediately followed by five minutes of iso-osmotic media containing 3H-glucose and 14 C-mannitol. Increased relative water content/decreased [glucose] (observed in HYPO-0) and decreased water content/increased [glucose] (observed in HYPER-0) returned to ISO levels within 5 minutes of recovery. Glycogen synthase percent activation increased significantly in HYPO-5 over iso-osmotic controls. Glucose uptake measurements revealed no significant differences between groups. It was determined that [glucose] and muscle water content rapidly recovered from osmotic stress demonstrating skeletal muscle's resilience to osmotic stress.

The effect of extracellular osmolality on cell volume and resting skeletal muscle metabolism

The purpose of the current investigation was to establish an in-l'itro skeletal muscle model to study acute alterations in resting skeletal muscle cell volume. Isolated. whole muscle (SOL and EDL) was dissected from Long Evans rats and incubated for 60 min in Sigma Medium-199 (resting tension (lg). bubbled with 95:5% 02:C02, 30 ± 2°C, and pH 7.4). Media osmolality was altered to simulate hypo-osmotic (190 ± 10 Osm) (HYPO) or hyper-osmotic conditions (400 ± 10 Osm) (HYPER) while an iso-osmotic condition (290± 1 0 Osm) (CON) served as a control (n= 17.19.17). Following incubation, relative muscle water content decreased with HYPER and increased with HYPO in both muscle types (p<0.05). The cross-sectional area of HYPO SOL type I and type II fibres increased (p<0.05) while the EDL type 11 fibre area decreased in HYPER and increascd from HYPO exposure. Furthermore, HYPER exposure in both muscles lead to decreased ATP and phosphocreatine (p<0.05) and increased creatine and lactate (p<0.05) compared to CON. This isolated skeletal muscle model proved viable and demonstrated that altering extracellular osmolality could cause acutc alterations in muscle water content and resting muscle metabolism.

The influence of skeletal muscle cell volume on carbohydrate metabolism in contracting skeletal muscle

This study investigated the regulation of carbohydrate metabolism through changes in skeletal muscle cell volume immediately post contraction and during recovery. Using an established in vitro isolated muscle strip model, soleus (SOL) and extensor digitorum longus (EDL) were dissected from male rats and incubated in an organ bath (perfused with 95% O2; 5% CO2, pH 7.4, temperature 25°C) containing medium- 199 altered to a target osmotic condition (iso-, hypo- or hyper-osmotic; 290, 1 80, 400 mmol/kg). Muscles were stimulated for 10 minutes (40 Hz SOL; 30 Hz EDL) and then either immediately flash frozen or allowed to recover for 20 minutes before subsequent metabolite and enzyme analysis. Results demonstrated a relative water decrease in HYPER vs. HYPOosmotic condition (n=8/group; p<0.05) regardless of muscle type. Specifically, the SOL HYPER condition had elevated metabolite concentrations after 10 minutes of stimulation in comparison to both HYPO and ISO (p<0.05), while EDL muscle did not show any significant difTerences between the HYPER or HYPO conditions. After 20 minutes of recovery, metabolic changes occurred in both SOL and EDL with the SOL HYPER condition showing greater relative changes in metabolite concentrations versus HYPO. The results of the current study have demonstrated that osmotic imbalance induces metabolic change within the skeletal muscle cell and muscle type may influence the mechanisms utilized for cell volume regulation.

Diatoms as indicators of lake trophic status

Relationships between surface sediment diatom assemblages and lake trophic status were studied in 50 Canadian Precambrian Shield lakes in the Muskoka-Haliburton and southern Ontario regions. The purpose of this study was to develop mathematical regression models to infer lake trophic status from diatom assemblage data. To achieve this goal, however, additional investigations dealing with the evaluation of lake trophic status and the autecological features of key diatom species were carried out. Because a unifying index and classification for lake trophic status was not available, a new multiple index was developed in this study, by the computation of the physical, chemical and biological data from 85 south Ontario lakes. By using the new trophic parameter, the lake trophic level (TL) was determined: TL = 1.37 In[1 +(TP x Chl-a / SD)], where, TP=total phosphorus, Chl-a=chlorophyll-a and SD=Secchi depth. The boundaries between 7 lake trophic categories (Ultra-oligotrophic lakes: 0-0.24; Oligotrophic lakes: 0.241-1.8; Oligomesotrophic lakes: 1.813.0; Mesotrophic lakes: 3.01-4.20; Mesoeutrophic lakes: 4.21-5.4; Eutrophic lakes: 5.41-10 and Hyper-eutrophic lakes: above 10) were established. The new trophic parameter was more convenient for management of water quality, communication to the public and comparison with other lake trophic status indices than many of the previously published indices because the TL index attempts to Increase understanding of the characteristics of lakes and their comprehensive trophic states. It is more reasonable and clear for a unifying determination of true trophic states of lakes. Diatom specIes autecology analysis was central to this thesis. However, the autecological relationship of diatom species and lake trophic status had not previously been well documented. Based on the investigation of the diatom composition and variety of species abundance in 30 study lakes, the distribution optima of diatom species were determined. These determinations were based on a quantitative method called "weighted average" (Charles 1985). On this basis, the diatom species were classified into five trophic categories (oligotrophic, oligomesotrophic, mesotrophic, mesoeutrophic and eutrophic species groups). The resulting diatom trophic status autecological features were used in the regressIon analysis between diatom assemblages and lake trophic status. When the TL trophic level values of the 30 lakes were regressed against their fi ve corresponding diatom trophic groups, the two mathematical equations for expressing the assumed linear relationship between the diatom assemblages composition were determined by (1) uSIng a single regression technique: Trophic level of lake (TL) = 2.643 - 7.575 log (Index D) (r = 0.88 r2 = 0.77 P = 0.0001; n = 30) Where, Index D = (0% + OM% + M%)/(E% + ME% + M%); 4 (2) uSIng a' multiple regressIon technique: TL=4.285-0.076 0%- 0.055 OM% - 0.026 M% + 0.033 ME% + 0.065 E% (r=0.89, r2=0.792, P=O.OOOl, n=30) There was a significant correlation between measured and diatom inferred trophic levels both by single and multiple regressIon methods (P < 0.0001, n=20), when both models were applied to another 20 test lakes. Their correlation coefficients (r2 ) were also statistically significant (r2 >0.68, n=20). As such, the two transfer function models between diatoms and lake trophic status were validated. The two models obtained as noted above were developed using one group of lakes and then tested using an entirely different group of lakes. This study indicated that diatom assemblages are sensitive to lake trophic status. As indicators of lake trophic status, diatoms are especially useful in situations where no local trophic information is available and in studies of the paleotrophic history of lakes. Diatom autecological information was used to develop a theory assessing water quality and lake trophic status.

Investigation of molecular polarizabilities and derivatives in halomethanes

The research undertaken was to obtain absolute Raman intensities for the symmetric stretching vibrations of the methyl halides, CH3X with (X=F, CI, Br), by experiment and theory. The intensities were experimentally measured using the Ar+ ion gas laser as excitation source, a Spex 14018 double monochromator and a RCA C-31034 photomultiplier tube as detector. These intensities arise from changes in the derivative of the polarizability (8 a'), with respect to vibration along a normal coordinate (8qi). It was intended that these derivatives obtained with respect to normal coordinates would be converted to derivatives with respect to internal coordinates, for a quantitative comparison with theory. Theoretical numerical polarizability derivatives for the stretching vibrations are obtained using the following procedure. A vibration was simulated in the molecule by increasi.ng and decreasing the respective bond by the amount ±o.oosA for the C-H bonds and ±o.oIA for the C-X (X=F, CI, Br) bond. The derivative was obtained by taking the difference in the polarizability for the equilibrium geometry and the geometry when a particular bond is changed. This difference, when divided by the amount of change in each bond and the number of bonds present results in the derivative of the polarizability with respect to internal coordinate i.e., !1u/!1r. These derivatives were obtained by two methods: I} ab initio molecular orbital calculation and 2} theory of atoms in molecules (AIM) analysis. Due to errors in the experimental setup only a qualitative analysis of the results was undertaken relative to the theory. Theoretically it is predicted that the symmetric carbonhalogen stretch vibrations are more intense than the respective carbon-hydrogen stretch, but only for the methyl chloride and bromide. The carbon fluorine stretch is less intense than the carbon-hydrogen stretch, a fact which is attributed to the small size and high electronegativity of the fluorine atom. The experimental observations are seen to agree qualitatively with the theory results. It is hoped that when the experiment is repeated, a quantitative comparison can be made. The analysis by the theory of atoms in molecules, along with providing polarizabilities and polarizability derivatives, gives additional information outlined below. The theory provides a pictorial description of the main factors contributing to the molecular polarizability and polarizability derivative. These contributions are from the charge transfer and atomic dipole terms i.e., transfer of charge from one atom to another and the reorganization of atomic electronic charge distribution due to presence of an electric field. The linear relationship between polarizability and molecular volume was also observed.

A five factor model of grief : a q-methodological study /

Q-methodology permitted 41 people to communicate their perspective of grief. In an attempt to clarify the research to date and to allow those who have experienced this human journey to direct the scientists, 80 statements were chosen to present to the participants based on the research from academic and counselling sources. Five different perspectives emerged from the Q-sorts and factor analysis. Each perspective was valuable for the understanding of different groups of mourners. They were interpreted using questionnaire data and interview information. They are as follows: Factor 1- Growth Optimism; Factor 2 - Schema Destruction and Negative Affect; Factor 3- Identification with the Deceased Person; Factor 4- Intact World view with High Clarity and High Social Support; Factor 5- Schema Destruction with High Preoccupation and Attention to Emotion. Some people grow in the face of grief, others hold on to essentially the same schemas and others are devastated by their loss. The different perspectives reported herein supply clues to the sources of these differing outcomes. From examination of Factor 1, it appears that a healthy living relationship helps substantially in the event of loss. An orientation toward emotions that encourages clarity, exemplified by Factor 4, without hyper-vigilance to emotion may be helpful as well. Strategies for maintaining schematic representations of the world with little alteration include: identification with the values of the deceased person, as in Factor 3 and reliance on social support and/or God as demonstrated by Factor 4. When the relationship had painful periods, social support may be accessed to benefit some mourners. When the person's frame of reference or higher order schemas are assaulted by the events of loss, the people most at risk for traumatic grief seem to be those with difficult relationships as indicated by Factor 5 individuals. When low social support, high attention to emotion with low clarity and little belief that feelings can be altered for the better are also attributes of the mourner devastating grief can result. In the end, there are groups of people who are forced to endure the entire process of schema destruction and devastation. Some appear to recover in part and others appear to stay in a form of purgatory for many years. The results of this study suggest that, those who experience devastating grief may be in the minority. In the future interventions could be more specifically addressed if these perspectives are replicated in a larger, more detailed study.

Sleep and information processing in individuals who have sustained a traumatic brain injury

Individuals who have sustained a traumatic brain injury (TBI) often complain of t roubl e sleeping and daytime fatigue but little is known about the neurophysiological underpinnings of the s e sleep difficulties. The fragile sleep of thos e with a TBI was predicted to be characterized by impairments in gating, hyperarousal and a breakdown in sleep homeostatic mechanisms. To test these hypotheses, 20 individuals with a TBI (18- 64 years old, 10 men) and 20 age-matched controls (18-61 years old, 9 men) took part in a comprehensive investigation of their sleep. While TBI participants were not recruited based on sleep complaint, the fmal sample was comprised of individuals with a variety of sleep complaints, across a range of injury severities. Rigorous screening procedures were used to reduce potential confounds (e.g., medication). Sleep and waking data were recorded with a 20-channel montage on three consecutive nights. Results showed dysregulation in sleep/wake mechanisms. The sleep of individuals with a TBI was less efficient than that of controls, as measured by sleep architecture variables. There was a clear breakdown in both spontaneous and evoked K-complexes in those with a TBI. Greater injury severities were associated with reductions in spindle density, though sleep spindles in slow wave sleep were longer for individuals with TBI than controls. Quantitative EEG revealed an impairment in sleep homeostatic mechanisms during sleep in the TBI group. As well, results showed the presence of hyper arousal based on quantitative EEG during sleep. In wakefulness, quantitative EEG showed a clear dissociation in arousal level between TBls with complaints of insomnia and TBls with daytime fatigue. In addition, ERPs indicated that the experience of hyper arousal in persons with a TBI was supported by neural evidence, particularly in wakefulness and Stage 2 sleep, and especially for those with insomnia symptoms. ERPs during sleep suggested that individuals with a TBI experienced impairments in information processing and sensory gating. Whereas neuropsychological testing and subjective data confirmed predicted deficits in the waking function of those with a TBI, particularly for those with more severe injuries, there were few group differences on laboratory computer-based tasks. Finally, the use of correlation analyses confirmed distinct sleep-wake relationships for each group. In sum, the mechanisms contributing to sleep disruption in TBI are particular to this condition, and unique neurobiological mechanisms predict the experience of insomnia versus daytime fatigue following a TBI. An understanding of how sleep becomes disrupted after a TBI is important to directing future research and neurorehabilitation.

TIME COURSE OF SIGNALING PROCESSES INVOLVED WITH EXTRACELLULAR OSMOTIC - INDUCED GLUCOSE UPTAKE IN MAMMALIAN SKELETAL MUSCLE

Extracellular hyper-osmotic (HYPER) stress increases glucose uptake to defend cell volume, when compared to iso-osmotic (ISO) conditions in skeletal muscle. The purpose of this study was to determine a time course for changes in common signaling proteins involved in glucose uptake during acute hyper-osmotic stress in isolated mammalian skeletal muscle. Rat extensor digitorum longus (EDL) muscles were excised and incubated in a media formulated to mimic ISO (290 ± 10 mmol/kg) or HYPER (400 ± 10 mmol/kg) extracellular condition (Sigma Media-199). Signaling mechanisms were investigated by determining the phosphorylation states of Akt, AMPK, AS160, cPKC and ERK after 30, 45 and 60 minutes of incubation. AS160 was found to be significantly more phosphorylated in HYPER conditions compared to ISO after 30 minutes (p<0.01). It is speculated that AS160 phosphorylation increases glucose transporter 4 (GLUT4) content at the cell surface thereby facilitating an increase in glucose uptake under hyper-osmotic stress.

Investigation of the Time Dependent Influence of Extracellular Osmotic Stress on Protein Turnover in Skeletal Muscle Cells

Acute alterations in cell volume can substantively modulate subsequent metabolism of substrates. However, how such alterations in skeletal muscle modulate protein metabolism is limited. The purpose of this study was to determine the time dependent influence of extracellular osmotic stress on protein turnover in skeletal muscle cells. L6 cells were incubated in hyperosmotic (HYPER; 425.3 ± 1.8mmol/kg), hypo-osmotic (HYPO; 235.4 ± 1.0mmol/kg) or control (CON; 333.5 ± 1.4mmol/kg) media for 4, 8, 12, or 24hrs. During the final 4hrs, incorporation of L-[ring-3,5-3H]-tyrosine was measured to estimate protein synthesis. Western blotting measured markers of protein synthesis and degradation. No differences were observed in any outcomes except p70S6K phosphorylation whereby HYPO was lower (p<0.05) than CON and HYPER; which remained similar except for a large increase at 8hrs for HYPER. These findings suggest that regardless of duration, extracellular osmotic stress does not significantly affect protein metabolism in L6 cells.

INFLUENCE OF INCREASED EXTRACELLULAR LEUCINE ON THE PROTEIN METABOLIC RESPONSES DURING OSMOTIC STRESS IN SKELETAL MUSCLE

The purpose of this study was to examine the effects of increased extracellular leucine concentration on protein metabolism in skeletal muscle cells when exposed to 3 different osmotic stresses. L6 skeletal muscle cells were incubated in either a normal or supplemental leucine (1.5mM) medium set to hypo-osmotic (230 ± 10 Osm), iso-osmotic (330 ± 10 Osm) or hyper-osmotic (440 ± 10 Osm) conditions. 3H-tyrosine was used to quantify protein synthesis. Western blotting analysis was performed to determine the activation of mTOR, p70S6k, ubiquitin, actin, and μ-calpain. Hypo-osmotic stress resulted in the greatest increase in protein synthesis rate under the normal-leucine condition while iso-osmotic stress has the greatest increase under the elevated-leucine condition. Elevated-leucine condition had a decreased rate in protein degradation over the normal condition within the ubiquitin proteasome pathway (p<0.05). Leucine and hypo-osmotic stress therefore creates a favourable environment for anabolic events to occur.

Bayesian Analysis for a Theory of Random Consumer Demand: The Case of Indivisible Goods

McCausland (2004a) describes a new theory of random consumer demand. Theoretically consistent random demand can be represented by a \"regular\" \"L-utility\" function on the consumption set X. The present paper is about Bayesian inference for regular L-utility functions. We express prior and posterior uncertainty in terms of distributions over the indefinite-dimensional parameter set of a flexible functional form. We propose a class of proper priors on the parameter set. The priors are flexible, in the sense that they put positive probability in the neighborhood of any L-utility function that is regular on a large subset bar(X) of X; and regular, in the sense that they assign zero probability to the set of L-utility functions that are irregular on bar(X). We propose methods of Bayesian inference for an environment with indivisible goods, leaving the more difficult case of indefinitely divisible goods for another paper. We analyse individual choice data from a consumer experiment described in Harbaugh et al. (2001).

Contamination des solutions d’hyper-alimentation intraveineuses (HAIV) néonatales, effet de l’ascorbylperoxyde au foie

Introduction : Chez les nouveau-nés prématurés, l’hyper-alimentation intraveineuse (HAIV) contribue à leur survie, mais elle est aussi une source importante de molécules oxydantes. L’absence d’une protection adéquate contre la lumière ambiante génère in vitro, via la photo-excitation de la riboflavine, du H2O2, des peroxydes organiques et un dérivé peroxydé de la vitamine C, l’ascorbylperoxyde (AscOOH). Plusieurs données du laboratoire associent l’infusion d’HAIV à des désordres lipidiques dans notre modèle animal. L’hypothèse est donc que l’AscOOH a un pouvoir oxydant et est responsable de certains des effets biologiques observés. Mes objectifs sont les suivants : 1) développer une méthode de dosage de l’AscOOH; 2) démontrer, à l’aide du modèle animal bien établi au laboratoire, des relations entre la concentration tissulaire de cette molécule et des paramètres métaboliques et l’état redox au foie et dans la circulation; et 3) confirmer l’effet physiologique de l’AscOOH dans un modèle cellulaire. Méthode : Différents étalons internes potentiels ont été testés pour le dosage de l’AscOOH par spectrométrie de masse après séparation sur HPLC (LC-MS). Les phases mobiles et conditions chromatographiques ont été optimisées. Pour l’objectif 2, des cobayes de 3 jours de vie (n=11) ont reçu par voie intraveineuse une dose d’AscOOH (entre 0 et 3,3mM). Les animaux ont été sacrifiés au 4e jour de traitement pour le prélèvement de tissus. Les concentrations tissulaires d’AscOOH ont été déterminées au LC-MS. La triglycéridémie et la cholestérolémie ont été mesurées à l’aide d’un kit commercial par spectrophotométrie. Le glutathion oxydé et réduit ont été mesurés par électrophorèse capillaire. Les relations linéaires obtenues sont exprimées par le ratio des carrés (r2), et traitées par ANOVA. Résultats : La validation du dosage de l’AscOOH par LC-MS a été réalisée. Chez les animaux, la concentration urinaire d’AscOOH par créatinine corrèle positivement avec la dose reçue, négativement avec la lipidémie, et négativement avec le redox sanguin et érythrocytaire, indiquant un milieu moins oxydé. Conclusion : La concentration urinaire d’AscOOH peut donc être un reflet de l’oxydation de l’HAIV en clinique. Nos données chez l’animal suggèrent une interaction de l’AscOOH avec le métabolisme hépatique produisant une chute de la concentration plasmatique de cholestérol et de triglycérides. Le modèle cellulaire n’a pas permis d’élucider le mécanisme moléculaire de l’action de l’AscOOH sur le métabolisme.

Influence de l’agrégation érythrocytaire sur la migration axiale de microparticules simulant des plaquettes sanguines

Lors du phénomène d’hémostase primaire ou de thrombose vasculaire, les plaquettes sanguines doivent adhérer aux parois afin de remplir leur fonction réparatrice ou pathologique. Pour ce faire, certains facteurs rhéologiques et hémodynamiques tels que l’hématocrite, le taux de cisaillement local et les contraintes de cisaillement pariétal, entrent en jeu afin d’exclure les plaquettes sanguines de l’écoulement principal et de les transporter vers le site endommagé ou enflammé. Cette exclusion pourrait aussi être influencée par l’agrégation de globules rouges qui est un phénomène naturel présent dans tout le système cardiovasculaire selon les conditions d’écoulement. La dérive de ces agrégats de globules rouges vers le centre des vaisseaux provoque la formation de réseaux d’agrégats dont la taille et la complexité varient en fonction de l’hématocrite et des conditions de cisaillement présentes. Il en résulte un écoulement bi-phasique avec un écoulement central composé d’agrégats de globules rouges avoisinés par une région moins dense en particules où l’on peut trouver des globules rouges singuliers, des petits rouleaux de globules rouges et une importante concentration en plaquettes et globules blancs. De ce fait, il est raisonnable de penser que plus la taille des agrégats qui occupent le centre du vaisseau augmente, plus il y aura de plaquettes expulsées vers les parois vasculaires. L'objectif du projet est de quantifier, in vitro, la migration des plaquettes sanguines en fonction du niveau d’agrégation érythrocytaire présent, en faisant varier l’hématocrite, le taux de cisaillement et en promouvant l’agrégation par l’ajout d’agents tels que le dextran à poids moléculaire élevé. Cependant, le comportement non Newtonien du sang dans un écoulement tubulaire peut être vu comme un facteur confondant à cause de son impact sur l’organisation spatiale des agrégats de globules rouges. De ce fait, les études ont été réalisées dans un appareil permettant de moduler, de façon homogène, la taille et la structure de ces agrégats et de quantifier ainsi leur effet sur la migration axiale des plaquettes. Du sang de porc anti coagulé a été ajusté à différents taux d’hématocrite et insérer dans un appareil à écoulement de Couette, à température ambiante. Les plaquettes sanguines, difficilement isolables in vitro sans en activer certains ligands membranaires, ont été remplacées par des fantômes en polystyrène ayant un revêtement de biotine. La quantification de la migration de ces fantômes de plaquettes a été réalisée grâce à l’utilisation de membranes biologiques fixées sur les parois internes de l’entrefer du rhéomètre de Couette. Ces membranes ont un revêtement de streptavidine assurant une très forte affinité d’adhésion avec les microparticules biotynilées. À 40% d’hématocrite, à un cisaillement de 2 s-1, 566 ± 53 microparticules ont été comptées pour un protocole préétabli avec du sang non agrégeant, comparativement à 1077 ± 229 pour du sang normal et 1568 ± 131 pour du sang hyper agrégeant. Les résultats obtenus suggèrent une nette participation de l’agrégation érythrocytaire sur le transport des fantômes de plaquettes puisque l’adhésion de ces derniers à la paroi du rhéomètre de Couette augmente de façon quasi exponentielle selon le niveau d’agrégation présent.