Kung-Ming Jan

Surface adsorption of dextrans on human red cell membrane

The adsorption isotherms of dextrans with molecular weights of 40,000 (Dx 40), 74,000 (Dx 70), and 450,000 (Dx 500) were studied on normal red blood cells (RBCs) and RBCs with surface charge depleted by neuraminidase treatment. The adsorption curves on neuraminidase-treated RBCs showed a two-step behavior with secondary adsorption commencing at a bulk concentration of approximately 5 g/100 ml. A plateau adsorption of approximately 9 × 10−14 g/RBC was attained with bulk concentrations between 12 and 20 g/100 ml. Normal RBCs showed similar adsorption curves as neuraminidase-treated RBCs in Dx 70, as well as in Dx 500, with bulk concentrations up to 5 g/100 ml. Further increases in bulk concentration of Dx 70 or Dx 500 caused greater adsorption on normal RBCs than on neuraminidase-treated RBCs, with a plateau concentration of approximately 15 × 10−14 g/RBC. Adsorption of Dx 40 on normal RBCs was higher than that on neuraminidase-treated RBCs at all bulk concentrations. These results on surface adsorption have been correlated with the aggregation behavior of the same cell systems. The data offer evidence in support of the hypothesis that surface adsorption of dextrans leads to RBC aggregation by bridging adjacent cell surfaces. The results also indicate that the adsorption of dextrans to RBC surface is a dynamic, reversible process in which the adsorbed molecules exchange readily with the molecules in the bulk or those attached to another cell surface. RBC aggregation is associated with an apparent decrease in surface adsorption as the opposing cell surfaces in the aggregate share their adsorption sites via the same dextran molecules.

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.

A Double Isotope Technique to Determine Regional Albumin Permeability: Effects of Anesthesia

Abstract The transvascular leakage of albumin in various organs and tissues was studied with a double isotope technique in rats anesthetized with sodium pentobarbital, given intraperitoneally or intravenously, and in unanesthetized (conscious) rats. 125I-labeled albumin and 131I-labeled albumin were injected into the tail vein 1 hr apart. The albumin permeability index in tissues and organs is indicated by the local ratio (Xa/Ya)/(Xb/Yb), where (Xa/Ya) is the ratio of 125I/131I-albumin activities per g of tissue and (Xb/Yb) is the ratio of 125I/131I-albumin activities per g of blood. If there is no passage of albumin across the capillary membrane over the 1-hr period of study, the permeability index will be equal to one. In unanesthetized rats, the liver, lung, kidney, femoral muscle, and femoral skin were regions with a high albumin permeability index (above 2). In these organs, intraperitoneal and intravenous anesthesia caused a decrease or no significant change of the albumin permeability index. There was no significant albumin leakage over 1-hr period (index not significantly different from 1) in the mesentery, abdominal muscle, abdominal skin, cremaster, heart, and brain of unanesthetized rats. Intraperitoneal anesthesia caused the albumin permeability index to increase to approximately 4 in the mesentery, abdominal muscle, and the abdominal skin, but not in the cremaster, heart, or brain. These results demonstrate that pentobarbital anesthesia when given into the peritoneal cavity causes a significant increase in albumin leakage in the abdominal region.

Beneficial or Detrimental Effects on Hemodynamics Depends on Dose of Dietary Potassium in Rapp Dahl Salt-Sensitive (DS) Rats.

P103 Dietary K supplementation was reported to lower blood pressure and prevent strokes in humans and to prevent strokes in hypertensive DS rats. We report a biphasic effect as a function of KCl dose in DS rats that were fed 1% NaCl with increasing dietary KCl, namely, 0.7, 2.6, 4, and 8%. After 8 months on 1% NaCl supplemented with 0.7% KCl, mean arterial pressure (MAP), plasma volume (PV), cardiac output (CO), total peripheral, renal and cerebral vascular resistances (TPR, RVR, CVR) increased compared to salt-resistant DR rats; on 2.6% KCl all these parameters decreased compared with DS on 0.7% KCl diet. When KCl was increased to 4 and 8%, MAP, PV, CO and RVR progressively increased in DS and DR rats, without changing TPR; these changes were accompanied by parallel increases in plasma aldosterone. Only DS rats on the ”optimal“ 2.6% KCl supplement maintained hemodynamics most similar to control DR rats and thus prevented Na retention, hypertension, increases in RVR and CVR. These beneficial hemodynamic effects may explain stroke prevention.

Electrochemical and Macromolecular Interactions at Red Blood Cell Surface

Red blood cells aggregate to form rouleaux in the presence of macro-molecules. Neutral and charged macromolecules were used to induce RBC aggregation quantified by microscopic observation. Variations of cell surface potential were achieved by the removal of RBC surface charge with neuraminidase treatment or by changing the ionic composition of the fluid medium. RBC aggregation by neutral polymer dextran is enhanced by removal of RBC surface charge and decreased by reduction of ionic strength. RBC aggregation by heparin requires the presence of sialic acids at cell surface and enhanced by reduction of ionic strength. It is concluded that the surface charge of RBCs plays a significant role in cell-to-cell interactions.