Biorheology - Volume 37, issue 4

Authors: Friedman, Morton H. | Henderson, Joel M. | Aukerman, Jean A. | Clingan, Paul A.

Article Type: Research Article

Abstract: Experiments were carried out in swine to test the hypothesis that changes in the fluid dynamic environment of the arterial wall, with time constants of several minutes to perhaps a few hours, prompt adaptive responses that transiently increase endothelial permeability. After parenteral Evans Blue Dye (EBD) administration, the hemodynamics of the external iliac arteries of the experimental animals were altered using a reversible arteriovenous femoral shunt. For 3 h, the shunt was opened and closed with a period (τ) between 1–180 min. Subsequently, the animal was euthanized and the iliac vessels were photographed en face to obtain the distribution of …EBD‐bound albumin uptake by the tissue during its exposure to the dye. Albumin uptake increases with τ in a fashion that can be explained by an a priori model of the adaptive permeability response, with a time constant of about an hour. Show more

Keywords: Shear effects, vascular permeability, albumin, time constant

Citation: Biorheology, vol. 37, no. 4, pp. 265-277, 2000

Authors: Wu, Ze‐Zhi | Zhang, Gang | Long, Mian | Wang, Hong‐Bin | Song, Guan‐Bin | Cai, Shao‐Xi

Article Type: Research Article

Abstract: The viscoelastic properties of both hepatocytes and hepatocellular carcinoma (HCC) cells were measured by means of a micropipette aspiration technique. Experimental results were analyzed with a three‐element standard linear solid model, 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, μ. Further, we investigated the relevance of viscoelastic properties of these two types of cells to the cytoskeleton structures by treating cells with three cytoskeletal perturbing agents, namely cytochalasin D (CD), colchicine (Col) and vinblastine (VBL). The results showed that the elastic …coefficients, but not viscous coefficient of HCC cells (K1 =103.6±12.6 N m−2 , K2 =42.5±10.4 N m−2 , μ=4.5±1.9 Pa s, n=30), were significantly higher than the corresponding values for hepatocytes (K1 =87.5±12.1 N m−2 , K2 =33.3±10.3 N m−2 , μ=5.9±3.0 Pa s, n=24). Upon treatment with CD, the viscoelastic coefficients of both hepatocytes and HCC cells decreased uniformly, with magnitudes for the decrease in elastic coefficients of HCC cells (K1 : 68.7 to 81.7 N m−2 , 66.3 to 78.9%; K2 : 34.5 to 37.1 N m−2 , 81.2 to 87.3%) larger than those for normal hepatocytes (K1 : 42.6 to 49.8 N m−2 , 48.7 to 56.9%; K2 : 17.2 to 20.4 N m−2 , 51.7 to 61.3%). There was a smaller decrease in the viscous coefficient of HCC cells (2.0 to 3.4 Pa s, 44.4 to 75.6%) than that for hepatocytes (3.0 to 3.9 Pa s, 50.8 to 66.1%). Upon treatment with Col and VBL, the elastic coefficients of hepatocytes generally increased or tended to increase while those of HCC cells decreased. The differences in either the pattern or the magnitude of the effect of cytoskeletal perturbing agent on the viscoelastic properties between HCC cells and hepatocytes might possibly reflect differences in the state of the cytoskeleton structure and function, or in the cells' sensitivity to perturbing agent treatment between these two types of cells. Changes in the viscoelastic properties of cancer cells might well affect tumor cell invasion and metastasis as well as interactions between tumor cells and their micro‐mechanical environments. Show more

Keywords: Hepatocytes, cytochalasin D, colchicine, vinblastine, micropipette aspiration, viscoelasticity

Citation: Biorheology, vol. 37, no. 4, pp. 279-290, 2000

Authors: Wang, Guixue | Cai, Shaoxi | Deng, Xiaoyan | Ouyang, Keqing | Xie, Guoming | Guidoin, Robert

Article Type: Research Article

Abstract: The shear‐induced secretory response of endothelin‐1 (ET‐1) by human microvascular endothelial cells was studied using paired human glomerular microvascular endothelial cell (HGMEC) cultured monolayers exposed to steady‐state laminar shear stress for up to 10 hours. The first cell monolayer was subjected to a shear stress of 0.65 N m−2 and the second, 1.3 N m−2 . ET‐1 secretion was determined by radioimmunoassay. Over 10 hours of shear, the total cumulative secretion of ET‐1 was 237.4 pg/cm2 for the monolayer exposed to 1.3 N m−2 and 143.6 pg/cm2 for the monolayer exposed to 0.65 N m−2 . …The average ET‐1 secretion rate was 20.90±2.15 and 12.45±1.05 pg/cm2 .h at 0.65 N m−2 and 1.3 N m−2 , respectively. The results showed that ET‐1 secretion varied with the time of shear in a nonlinear fashion. Although the level of shear stress affected the absolute value of ET‐1 cumulative secretion and secretion rate, the major secretion period for both monolayers occurred between 2.0 and 8.0 hours, with the peak secretion rate occurring at approximately 5 hours. Thus, the response of cultured human microvascular endothelial cells to shear stress differed from that of large vessel endothelial cell cultures in terms of ET‐1 secretion. In addition to the level of shear stress, the time of shear was also an important determinant of ET‐1 secretion. Consequently, the heterogeneity of vascular endothelial cells and the time of shear should both be considered in future research on the secretion of vascular endothelial cell cultures. Show more

Keywords: Shear stress, microvascular endothelial cells, endothelin‐1, cellular secretion

Citation: Biorheology, vol. 37, no. 4, pp. 291-299, 2000

Authors: Toth, K. | Wenby, R.B. | Meiselman, H.J.

Article Type: Research Article

Abstract: Previous reports have suggested that non‐ionic poloxamer surfactants of appropriate molecular mass and composition can reduce red blood cell (RBC) aggregation in whole blood and in RBC‐plasma suspensions. We have thus evaluated this phenomenon for RBC aggregated by several water‐soluble polymers, using poloxamer 188 (P188), a non‐ionic, tri‐block molecule (total molecular mass of 8.40 kDa, 80% polyoxyethylene). Human RBC were washed, then re‐suspended in isotonic solutions of dextran 70 (70.3 kDa), dextran 500 (476 kDa), PVP (360 kDa) or P‐L‐GLU (61.2 kDa); density‐separated RBC were also studied. RBC aggregation was quantitated via a computerized Myrenne Aggregometer (extent, strength) and by …the Microscopic Aggregation Index (MAI) method. Over the range of 0.5 to 5 mg/ml, poloxamer 188 inhibited both the extent and strength of aggregation in a dose‐dependent manner, with the magnitude of the decrease related to polymer type (e.g., at 5 mg/ml, 62% decrease for dextran 70 vs. 14% decrease for P‐L‐GLU); MAI results with dextran 70 also showed a dose‐dependent decrease. Poloxamer 188 at 5 mg/ml was more effective with younger, less‐dense cells. Based upon the depletion model for polymer‐induced aggregation, these findings suggest that poloxamer 188 acts by penetrating the depletion layer near the glycocalyx, thereby reducing the osmotic gradient between the intercellular gap and the suspending medium. Regardless of the specific mechanism(s) of action, poloxamers appear to offer interesting approaches for future basic science and clinical studies, and thus the possibility for greater insight into RBC aggregation. Show more

Citation: Biorheology, vol. 37, no. 4, pp. 301-312, 2000

Authors: Pohl, Manfred | Wendt, Max O. | Koch, Brigitte | Vlastos, George A.

Article Type: Research Article

Abstract: Human or animal blood is normally used as a test fluid for the in vitro evaluation of hemolysis by artificial organs. However, blood has some disadvantages (large biological variability and problems with cleaning the devices). For that reason, we searched for a reproducible technical fluid with blood‐like flow characteristics that exhibits similar shear depending destruction. In this study, a direct comparison between erythrocyte damage of bovine blood and shear‐induced degradation of polyacrylamide solution is given. A uniform shear field was applied to the fluids using a shear device with a plate‐plate geometry. It was shown that similarities exist between …erythrocytes disaggregation and breakdown of super molecular structures in polymer solutions, caused by mechanical stress. In both cases steady low shear viscositity was diminished and the elastic component of complex viscosity of blood and polymer solutions has been reduced. There is a correlation between shear‐induced hemolysis of bovine blood and mechanical polymer‐degradation, which depends on the applied shear stresses. Show more

Citation: Biorheology, vol. 37, no. 4, pp. 313-324, 2000