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Biomedical subjects

S Chien

Publications and source records attributed to S Chien.

At least 235 records · Page 13Linked to original sources
PubMed1984

Viscoelastic properties of leukocytes.

The viscoelastic properties of leukocytes (WBCs) during small deformation were determined by micropipette aspiration. The passive deformation behavior of neutrophils suspended in a Ca2+-free medium in response to a step aspiration pressure consists of an initial rapid, elastic response followed by a creep displacement. These time-dependent responses can be modeled by a viscoelastic solid in which an elastic element (K1) is in parallel with a Maxwell element composed of another elastic element (K2) in series with a viscous element (mu). Variations in temperature (9-40 degrees C) cause an inverse change in mu, but have no effects on K1 and K2. All three coefficients are not affected by decreases in pH down to 5.4; with pH greater than or equal to 7.8, however, K1 and mu increase. Increases in osmolality cause a rise in all three coefficients, especially mu. Colchicine treatment results in selective decreases in mu and K2 without affecting K1. B lymphocytes have viscoelastic coefficients similar to those of neutrophils, but T lymphocytes have higher values for these coefficients. In the presence of 2 mM Ca2+, the neutrophils have higher viscoelastic coefficients than in Ca2+-free medium, and they form protopods which have greater resistance than the main cell body to deformation by micropipette aspiration. Morphometric analysis shows that WBCs have large excess membrane area due to the presence of membrane foldings, which facilitate WBC deformation at constant area. During filtration through 5-micrometers sieves, WBCs are much more prone to pore plugging than erythrocytes because of their higher cellular viscosity and the presence of nucleus. The rheological properties of WBCs have significant implications in their functions and flow dynamics in the microcirculation.

Colchicine↗
PubMed1984

Rheologic measurements on small samples with a new capillary viscometer.

A newly developed capillary viscometer (capillary diameter 496 micron, length 10 cm) was tested and used for measurement of blood viscosity. The determination of pressure drop along the capillary during a constant flow allowed the calculation of the apparent viscosity. By changing the flow rate, the shear rate could be varied from 0.67 to 590 sec-1. A sample of 0.5 ml was sufficient for readings to be made at 10 shear rates in this range. Measurements of distilled water and standard oils were in good agreement with the expected values. Measurements on adult human plasma and umbilical cord blood were compared with simultaneous readings by Couette viscometer. For whole blood at various shear rates, regression analysis between the viscosity obtained from the capillary viscometer and that from the Couette viscometer yielded excellent correlation (r = 0.968, p less than 0.001). This capillary viscometer with high precision for very small samples is useful for various clinical applications.

Adult↗
PubMed1984

Evaluation of red blood cell filterability test: influences of pore size, hematocrit level, and flow rate.

To improve understanding of the basic principles of the red blood cell filtration test, we studied the influence of pore size, flow rate, and hematocrit level. Suspensions of washed red blood cells in Ringer's solution with hematocrit values of 5%, 10%, and 15% were pumped at flow rates of 0.42 and 0.82 ml/min through polycarbonate filters with pore sizes of 2.6 +/- 0.2, 4.5 +/- 0.6, and 6.9 +/- 0.8 micron (mean +/- SD). The initial pressure generated at the filter was normalized for pressure reading obtained with cell-free Ringer's solution at the same flow rate and used for the calculation of the relative resistance of one red blood cell in a pore. This measurement was independent of the flow rate and the hematocrit level, but it varied inversely with the pore size: 175.1 +/- 62.5, 5.2 +/- 1.2, and 2.4 +/- 0.8 for the 2.6, 4.5, and 6.9 micron pores, respectively. Plugging of filter pores as evidenced by progressive pressure rise at constant flow was a prominent feature for 2.6 micron filters, but was not significant for 6.9 micron filters. At the flow rates studied, less than 1% of the filtered red blood cells showed morphologic changes or underwent hemolysis. We found that 2.6 micron filters are most sensitive in detecting altered red blood cell filterability induced in vitro and occurring in vivo. These results may help to define an optimum filtration test for clinical investigations.

Adult↗
PubMed1984

Filterability of subpopulations of leukocytes: effect of pentoxifylline.

Human leukocytes were separated by density into two fractions, one containing predominantly granulocytes (FI) and the other, lymphocytes and monocytes (FII). The filterability of these fractions and their mixture was determined from the pressure measured during constant flow through 5-microns Nuclepore filters. The pressure-time curve of FI indicates the behavior of a relatively homogeneous cell population. The FII pressure-time curve can be analyzed to distinguish the effect of the more numerous and more filterable lymphocytes from that of the sparser but less filterable monocytes. Pressure generated by mixed leukocytes, which had been treated with 1 and 10 mmol/L of pentoxifylline (PTX) or its metabolite I, was substantially less than untreated control; at 10 mmol/L, the pressure was reduced to about 50% of control. PTX appears to affect the filterability of monocytes and polymorphonuclear leukocytes but not lymphocytes. Scanning electron microscopy showed an inhibition of protopod formation in the treated granulocytes. The degree of cell adhesion to the filter, as measured by the number of cells remaining on the outflow side of the filter, was similar in all groups (FI and FII, treated and untreated). The results indicate that the variations in filterability between the leukocyte subpopulations and the improvement by PTX treatment reflect differences in the cells' ability to deform under the test conditions.

Cell Separation↗
PubMed1983

Measurement of blood flow in the dental pulp of dogs with the 133xenon washout method.

Following rapid injection of 133Xe into the maxillary artery, the radioactivity from a dog canine tooth was monitored with a specially-designed scintillation probe connected to a multichannel analyser. With a PDP 11/10 minicomputer, the semilogarithmic radioactivity-time curve was resolved into a fast component and a slow component using best fit least-square lines and the exponential rate constant (k) was determined for each component. The blood flow per unit of pulp mass (Q, in ml/min per 100 g) was obtained using the equation: Q = k X lambda tb, where lambda tb is the tissue-blood partition coefficient of 133Xe in the pulp determined for the haematocrit value of the individual experiments. The fast-component blood flow was 53.12 +/- 3.12 and the slow-component blood flow was 8.86 +/- 0.53 ml/min per 100 g (mean +/- SEM, n = 21). Although the exact anatomical areas for the fast and slow components are yet to be determined, the results show heterogeneity of blood flow in the pulp. The study showed that pulp blood flow in an intact tooth can be measured with the 133Xe washout method; the method enables study of circulatory physiology of the pulp in health and disease.

Animals↗
PubMed1983

Influence of cholesterol content on red cell membrane viscoelasticity and fluidity.

The purpose of this investigation was to correlate the viscoelastic properties and lipid fluidity of the red blood cell membrane to its lipid composition. The viscoelastic properties of human red cells that had been enriched or depleted in cholesterol were determined by the micropipette technique. The lipid fluidity of the outer and inner leaflets of the erythrocyte membrane was concurrently assessed by steady state fluorescence depolarization. The elastic modulus and the viscosity moduli of the erythrocyte membrane showed no significant differences between the cholesterol-modified and the control cells. Cholesterol enrichment decreased the lipid fluidity of the outer membrane leaflet alone, and cholesterol depletion increased the fluidity mainly of the inner leaflet.

Cholesterol↗
PubMed1983

Ultrastructural visualization of low-density lipoproteins during receptor binding and cellular endocytosis.

Human fibroblasts possess surface receptors which have a high affinity for low-density lipoproteins (LDL). However, previous studies have not provided direct ultrastructural visualization of LDL bound to the receptor. To permit direct observation of unlabeled LDL during receptor binding and cellular endocytosis, we examined several fixative regimens which employ lipophilic stains. Staining with tannic acid, an oxidized form of ruthenium red, or potassium ferrocyanide imparted sufficient contrast to individual molecules of LDL to permit high-resolution electron microscopy of receptor binding and endocytosis. The LDL molecule was observed in immediate contact with the receptor and the coated vesicle, indicating that receptor-ligand binding occurs by short-range interactions.

Cell Membrane↗
PubMed1983

Ultrastructure of hepatic cholesterol crystals in the hypercholesterolemic - diabetic rat.

The cellular morphology of lipid accumulation in the liver was examined in normal rats fed a diet containing cholesterol and cholic acid, and streptozotocin-diabetic rats fed the same diet. The cholesterol-fed non diabetic rats displayed moderate hypercholesterolemia (average cholesterol 317 mg/dl) whereas the cholesterol-fed diabetic rats exhibited severe hypercholesterolemia (cholesterol greater than 1300 mg/dl). Ultrastructural studies were performed on hepatic tissues following in situ fixation and water soluble embedment, which were used to reduce lipid extraction and minimize structural distortions. Although both groups exhibited hepatocyte lipid droplets, the accumulation was markedly accentuated in the diabetic animals. The Kupffer cells of the diabetic animals contained cytosolic lipid crystals that were membrane delimited and showed lattice ordering 3.9 +/- 2.2 nm periodicity. These findings suggest that cholesteryl ester crystals of the cholesteric phase, similar to those found in atherosclerotic lesions, may form in other cellular foci exposed to abnormally high plasma lipid levels.

Animals↗
PubMed1983

Theoretical models of rouleau formation and disaggregation.

The formation of rouleaux of red blood cells is considered as an interaction of the surface adhesive energy and the elastic strain energy of the red blood cell membrane. A dynamic energy equation is written which applies to both the process of aggregation and the disaggregation by external forces. Any equilibrium state may be regarded as minimization of the appropriate energy potentials. The theory is illustrated by the computation of the shapes of two cell rouleaux under different surface adhesive energies. Disaggregation is studied in a model in which the red blood cells are idealized as cylindrical forms. It is shown that during disaggregation the strain energy stored in the cell contributes to the work done in overcoming the adhesive energy.

Cell Adhesion↗
PubMed1983

Energy balance in red cell interactions.

Experiments were performed to elucidate the balance of energies involved in the formation of red blood cell (RBC) aggregates and in their disaggregation. In order to achieve a mean stable rouleau formation, the aggregating energy provided by macromolecular binding to the cell membrane must overcome the disaggregation energy of electrostatic repulsion between RBC surfaces and the effects of mechanical shear stress. In a quiescent suspension the net aggregation energy is largely stored in the membrane as a change in strain energy. The alterations in strain energy cause the curvature of the end cells in rouleaux of normal RBCs in Dx 80 to change from concave to convex and back again to concave as [Dx 80] was increased from 1 to 4 to 6 g/dl; computation of net aggregation energy per unit area (gamma) from changes in membrane strain energy yielded values on the order of 10(3) ergs/cm2. The end cells of neuraminidase-treated RBCs remained convex with [Dx 80] above 2 g/dl, and gamma is probably on the order of 10(2) ergs/cm2. The variations in gamma with [Dx 80] and RBC surface charge are similar to variations in reflectometric aggregation index without shear ( RAI0 ), indicating that RAI0 reflects gamma. The difference in gamma between normal and neuraminidase-treated RBCs represents the electrostatic repulsive energy, the magnitude of which varied inversely with dextran molecular size and directly with [Dx]. Moderate shearing in the reflectometer enhanced RBC aggregation by promoting cell-cell encounter, but high shear stresses cause RBC disaggregation. The energy required to disaggregate a unit interacting area of normal RBCs in Dx 80 in a flow channel is on the order of 10(4) ergs/cm2, which is much lower than gamma. These results suggest that the release of the stored membrane strain energy during disaggregation aids in the separation process. The results show that the understanding of RBC aggregation requires the considerations of surface charge, properties of aggregating agents, and the rheology of the cell membrane.

Dextrans↗
PubMed1983

Effects of variations in renal hemodynamics on the time course of renin secretion rate.

The effects of variations in renal hemodynamics on the time course of renin secretion were studied in dogs anesthetized with pentobarbital-chloralose. Hemodynamic changes were induced either locally in kidneys perfused in situ via an extracorporeal circuit (with or without a pump system) or systemically by hemorrhage or nitroprusside infusion. In the autoperfused kidney the reduction of renal perfusion pressure to approximately one-half of the arterial pressure by inflow occlusion caused an increase in renal conductance (renal vasodilation) and an increase in renin secretion rate (RSR). In the pump-perfused kidney, a step increase in renal blood flow (RBF) caused renal vasoconstriction and a decrease in RSR; a step decrease in RBF caused renal vasodilation and an increase in RSR. Following step changes in RBF, the time constant of the alterations of renal conductance was 56.5 s, and the time constant of the RSR responses was 80.1 s. The total time required to reach a steady state for RSR lagged behind that for renal conductance by approximately 5 min. These differences reflect the time needed for the kidney to release renin in response to changes in renal vascular caliber. The results suggest that renin release occurs in response to the autoregulatory dilation of the renal arterioles. When systemic hypotension was induced by nitroprusside infusion, RSR also increased together with the renal conductance. Following hemorrhage, however, RSR increased despite a decrease in renal conductance, reflecting the role of neurohumoral factors in causing renin release in this case. The comparison of renin secretion following different types of hemodynamic alterations serves to elucidate the mechanisms of renin secretion.

Animals↗
PubMed1983

Colloidal gold: a pluripotent receptor probe.

Colloidal gold is an electron-dense, lyophobic colloid that readily forms a stable electrostatic interaction with a variety of macromolecules. Monodispersed colloids ranging from 3-150 nm in diameter can be produced to provide the researcher with flexibility in selecting the optimally sized probe. Gold labeling of antibodies and lectins has been extensively used to study surface antigens and cell components. Recently, the use of gold labeling has been extended to study receptor-ligand binding, enzyme-substrate reactions, and transcellular pathways. Published applications include gold labeling of metabolites (low-density lipoproteins), enzymes (DNAase and RNAase, RNA polymerase, thrombin, collagenase, elastase), hormones (insulin, epidermal growth factor, glucagon), circulating plasma proteins (asialoglycoprotein, alpha 2-macroglobulin, factor VIII-von Willebrand factor), and endotoxins (tetanus toxin, cholera toxin). This broad spectrum of applications emphasizes the versatility and usefulness of colloidal gold as a probe in areas of cell biology related to receptors, endocytosis, transport, and functions of proteins.

Animals↗
PubMed1983

Role of white blood cells in filtration of blood cell suspensions.

The time-dependent filtration pressure curves of cell suspensions pumped through 5 microns polycarbonate filters at a constant flow rate were analyzed with the aid of a theoretical model developed in an accompanying paper. The cell suspensions contained mixtures of erythrocytes and leukocytes, the concentrations of which were systematically varied. The pressure-time (P-t) curves generally showed multiphasic components. Following the attainment of a quasi-steady state level, the pressure rose first rapidly and then more slowly. The rates of pressure rise in the fast and slow phases were normalized by using the steady state pressure reading (PO) obtained with Ringer solution at the same flow rate, and are designated k1 and k2, respectively. Both k1 and k2 increased with rising concentrations of leukocytes, [WBC], or erythrocytes, [RBC]. [WBC] is 700-1000 times more effective than [RBC] in affecting k1 and k2. k1 is related to the dynamic plugging and unplugging of filter pores, primarily by leukocytes. k2 is attributable to the "permanent" plugging of filter pores, again predominantly by leukocytes. The experimental P-t curves can be fitted with the theoretical model by using appropriate constants for leukocyte plugging. The results indicate that nearly 2/3 of the entering leukocytes cause transient plugging of pores, with an unplugging rate of 4.1 percent/sec/unit pressure rise, and that approximately 2.2 percent of the entering leukocytes are "permanently" lodged. These results underscore the important role of leukocytes in determining the later phase of the P-t curve and support the concept that leukocyte plugging may have pathophysiological significance in causing microvascular occlusion in disease states.

Erythrocytes↗
PubMed1983

Influence of red cell concentration on filtration of blood cell suspensions.

Pressure-time curves obtained by passing suspensions of blood cells in Ringer solution through a 5 microns polycarbonate filter at constant flow (1.6 ml/min) were evaluated for their ability to reflect the deformability of the erythrocytes. The initial pressure reading (Pi) obtained in a quasi-steady state during the first 1-2 sec of pumping was found to be reproducible for hematocrit values between 10 and 30 percent. This Pi value was normalized by the pressure generated by the cell-free suspending medium (PO) at the same flow rate. The ratio Pi/PO was found to be linearly proportional to hematocrit up to 30 percent but independent of leukocyte concentration up to 12,000/mm3. Later portions of the curve did vary with leukocyte count. By using the equations developed from theoretical modeling of cells passing through a filter, the experimentally determined relation of Pi/PO to hematocrit, and the known geometry of the filter pores, we were able to calculate parameters reflecting the deformability of red cells. These include beta, the ratio of resistance in a pore containing a red cell to that in a pore containing only the suspending medium, and alpha, the proportion of pores filled by erythrocytes in transit. The application of theoretical analysis to experimental data has provided quantitative insights into the behavior of red cells during filtration tests in normal and disease states.

Erythrocytes↗
PubMed1983

Theoretical modeling of filtration of blood cell suspensions.

A theoretical model of filtration of suspensions containing red blood cells (RBCs) and white blood cells (WBCs) has been developed. Equations are written for the pressure drop, the filtration flow and the fractions of filter pores containing RBCs (alpha) and WBCs (alpha*). Because the relative resistances (ratios of resistance of cell to resistance of suspending fluid) of RBCs (beta) and WBCs (beta*) through the filter pore are greater than one, the transit of these cells (especially WBCs) through the filter is slower than that of suspending fluid; this leads to values of alpha and alpha* higher than those simply expected from the hematocrit and leukocrit, respectively, in the entering and exiting suspensions. In the absence of pore plugging by the cells (steady flow), the pressure drop can be computed from alpha, alpha*, beta and beta*. In order to model unsteady flow, differential equations are written to include pore plugging and the subsequent unplugging by the rising filtration pressure at a constant flow. By specifying the fractions of entering RBCs (epsilon) and WBCs (epsilon*) which would plug the pores and the rate at which the plugged pores would unplug in response to pressure rise (epsilon u), as well as the fractions of entering RBCs (epsilon p) and WBCs (epsilon p*) that would plug the pores permanently, theoretical pressure-time curves can be generated by numerical integration, and the results fit the experimental data well. From such fitting of theoretical curve to experimental data, information can be deduced for epsilon, epsilon*, epsilon u, epsilon p and epsilon* p.

Erythrocytes↗
PubMed1983

The bulk rheology of close-packed red blood cells in shear flow.

A theoretical analysis is made of the dynamical behavior and bulk rheology of close-packed red blood cell suspensions subjected to simple shear flow. The model for the polyhedral cell shapes and tank-treading membrane motion developed in the companion paper (1) is used. The flow in the thin lubricating plasma layers between cells is analyzed taking into account the mechanical properties of the membrane at the corner regions of sharp membrane curvature. This leads to predictions for the apparent viscosity as a function of hematocrit and shear rate. Good agreement with experimental results is obtained at moderate and high shear rates (above 20 s-1). At lower shear rates, a rapid rise in apparent viscosity has been found experimentally, and the mechanisms leading to this behavior are examined.

Blood Viscosity↗