The hemolytic volume of human erythrocytes

My Passion and Passages with Red Blood Cells

This article mainly presents, in sequential panels of time, an overview of my professional involvements and laboratory experiences. I became smitten with red blood cells early on, and this passion remains with me to this day. I highlight certain studies, together with those who performed the work, recognizing that it was necessary to limit the details and the topics chosen for discussion. I am uncertain of the interest a personal account has for others, but at least it's here for the record.

Cardiac cell volume: crystal clear or murky waters? A comparison with other cell types

The osmolarity of bodily fluids is strictly controlled so that most cells do not experience changes in osmotic pressure under normal conditions, but osmotic changes can occur in pathological states such as ischemia, septic shock, and diabetic coma. The primary effect of a change in osmolarity is to acutely alter cell volume. If the osmolarity around a cell is decreased, the cell swells, and if increased, it shrinks. In order to tolerate changes in osmolarity, cells have evolved volume regulatory mechanisms activated by osmotic challenge to normalise cell volume and maintain normal function. In the heart, osmotic stress is encountered during a period of myocardial ischemia when metabolites such as lactate accumulate intracellularly and to a certain degree extracellularly, and cause cell swelling. This swelling may be exacerbated further on reperfusion when the hyperosmotic extracellular milieu is replaced by normosmotic blood. In this review, we describe the theory and mechanisms of volume regulation, and draw on findings in extracardiac tissues, such as kidney, whose responses to osmotic change are well characterised. We then describe cell volume regulation in the heart, with particular emphasis on the effect of myocardial ischemia. Finally, we describe the consequences of osmotic cell swelling for the cell and for the heart, and discuss the implications for antiarrhythmic drug efficacy. Using computer modelling, we have summated the changes induced by cell swelling, and predict that swelling will shorten the action potential. This finding indicates that cell swelling is an important component of the response to ischemia, a component modulating the excitability of the heart.

Activation of ion transport pathways by changes in cell volume

Swelling-activated K+ and Cl- channels, which mediate RVD, are found in most cell types. Prominent exceptions to this rule include red cells, which together with some types of epithelia, utilize electroneutral [K(+)-Cl-] cotransport for down-regulation of volume. Shrinkage-activated Na+/H+ exchange and [Na(+)-K(+)-2 Cl-] cotransport mediate RVI in many cell types, although the activation of these systems may require special conditions, such as previous RVD. Swelling-activated K+/H+ exchange and Ca2+/Na+ exchange seem to be restricted to certain species of red cells. Swelling-activated calcium channels, although not carrying sufficient ion flux to contribute to volume changes may play an important role in the activation of transport pathways. In this review of volume-activated ion transport pathways we have concentrated on regulatory phenomena. We have listed known secondary messenger pathways that modulate volume-activated transporters, although the evidence that volume signals are transduced via these systems is preliminary. We have focused on several mechanisms that might function as volume sensors. In our view, the most important candidates for this role are the structures which detect deformation or stretching of the membrane and the skeletal filaments attached to it, and the extraordinary effects that small changes in concentration of cytoplasmic macromolecules may exert on the activities of cytoplasmic and membrane enzymes (macromolecular crowding). It is noteworthy that volume-activated ion transporters are intercalated into the cellular signaling network as receptors, messengers and effectors. Stretch-activated ion channels may serve as receptors for cell volume itself. Cell swelling or shrinkage may serve a messenger function in the communication between opposing surfaces of epithelia, or in the regulation of metabolic pathways in the liver. Finally, these transporters may act as effector systems when they perform regulatory volume increase or decrease. This review discusses several examples in which relatively simple methods of examining volume regulation led to the discovery of transporters ultimately found to play key roles in the transmission of information within the cell. So, why volume? Because it's functionally important, it's relatively cheap (if you happened to have everything else, you only need some distilled water or concentrated salt solution), and since it involves many disciplines of experimental biology, it's fun to do.

Interaction of free fatty acids with the erythrocyte membrane as affected by hyperthermia and ionizing radiation

The interference of hyperthermia and ionizing radiation, respectively, with the effects of capric (10:0), lauric (12:0), myristic (14:0), oleic (cis-18:1) and elaidic (trans-18:1) acids on the osmotic resistance of human erythrocytes was investigated. The results are summarized as follows: (A) not only at 37 degrees, but also at 42 degrees and 47 degrees C lauric acid (12:0) represents the minimum chain length for the biphasic behaviour of protecting against hypotonic hemolysis at a certain lower concentration range and hemolysis promotion at subsequent higher concentrations; (B) with increasing temperatures the protecting as well as the hemolytic effects occur at lower concentrations of the fatty acids; (C) the increase of temperature promotes the extent of hemolysis and reduces the extent of protection against hypotonic hemolysis; (D) Gamma-irradiation of erythrocytes selectively affects the concentration of oleic acid at which maximum protection against hypotonic hemolysis occurs, without altering the minimum concentration for 100% hemolysis.

Measurement of biophysical properties of red blood cells by resistive pulse spectroscopy: volume, shape, surface area, and deformability

This paper presents a simple, new approach to the determination of size, shape, surface area, and deformability information for cells, notably red blood cells. The results are obtained by combining experimental measurements from resistive pulse spectroscopy (an extension of electronic cell-sizing methodology) with theoretical calculations for model cell systems. Assuming constancy of surface area and approximating red cell shapes by both prolate and oblate ellipsoids of revolution, values are determined for cell shape factor and volume under a variety of conditions. For red blood cells under low-stress conditions, shape factor, volume, and surface area results are found to be consistent with those available from the literature, when the oblate model is used. The applicability of this approach for determination of red cell properties under altered conditions is demonstrated by results for cell volume, at varying osmotic pressure and mechanical shear (tensile) stress. By quantitating the change in cell shape with stress, a new numerical scale for measuring cell deformability is also obtained, and data are presented on its variation for red cells at different osmolalities, over the range of 140 to 500 mOsm.

Temperature effects on osmotic fragility, and the erythrocyte membrane

Results are reported on the temperature-dependence of intact-cell surface area, isotonic volume, hemolytic volume, and ghost steady-state surface area and volume, using several techniques of resistive pulse spectroscopy. Temperature was found not to alter the intact cell surface area permanently: the area remains constant at 130 +/- 1 micron 2, at temperatures ranging from 0 to 40 degrees C. Temperature does alter the steady-state volume of the cells, with a colder temperature inducing swelling by about 0.29 micron 3/deg. C. Such a temperature-induced volume change is sufficient to explain only approximately half of the fragility differences which result from temperature changes. The remainder was found to result from higher temperatures enabling a substantial transient increase in surface area of intact cells (up to at least 14% of 40 degrees C), with a corresponding increase in the cell's hemolytic volume (up to 21%). The hemolytic volume apparently increases linearly with temperature, since steady-state ghost volumes are found to increase linearly with the temperature at which the ghosts were produced. In the steady state (at high temperature), the membranes of electrically-impermeable resealed ghosts can remain extended by more than 10%, compared with membranes of the corresponding unhemolyzed, intact red cells.

Jet expulsion of cellular contents from rad cells during photodynamic hemolysis

When red cells are incubated in the dark in the presence of the dye Rose Bengal and subsequently irradiated with visible light, they hemolyze. Under certain conditions some of the hemoglobin is expelled in the form of a convective jet and appears as a transient cloud beside the cell. Elastic contraction of the membrane is not a sufficient driving force for the jet. A plausible mechanism (an osmotic "pump") is presented.

Membrane and intracellular modes of sugar-dependent increments in red cell stability

Sugar-dependent increments in red cell stability under osmotic stress can be ascribed to changes either in the membrane or in the intracellular matrix. These two possible modes of action have been tested and characterized. Rheological investigation of membrane-free haemoglobin solutions has shown that D-glucose, but not D-fructose, promotes the formation of a visco-plastic gel structure. Gel strength is a function of glucose concentration, haemoglobin concentration and temperature. The ability of various sugars to promote gel formation correlates with their solution properties. The existence of gel structure reduces K+ and haemoglobin leak from red cells whose membranes were partially destroyed by gamma-radiation. Reduced osmotic swelling in the presence of glucose is also due to gel formation since the glucose effect is lost in resealed red cell ghosts. D-Fructose does not protect red cells against radiation damage; its mode of action in increasing red cell stability under osmotic stress is a membrane effect. Cell sizing using the Coulter Counter has shown that fructose, but not glucose, can increase the maximal volume at lysis. At 50 mM, D-fructose expands the red cell ghost volume by 11.2%; this represents a 7.2% increase in membrane area. Ghost expansion by fructose is fructose concentration dependent (0-100 mM) and is insensitive to temperature variation (0-37 degrees C).

Distribution of size and shape in populations of normal human red cells

The diameter, area, and volume of individual human erythrocytes (of 8 subjects, newborn to age 71) were determined by photographing the cells hanging on edge. Measurements from high magnification prints were processed by computer. The distributions of diameter, area, and volume are described statistically, with the unexpectedly linear regression equations for their interrelations. The plot of area vs. volume for the 1016 normal cells from seven subjects (newborn excluded) was remarkably linear with a "straight-line" boundary restricting the distribution. Shape was characterized by a dimensionless "sphericity index" (4.84.volume 2/3 /area). Cells of larger volume tended to be thinner than the smaller cells.

The red cell can easily be deformed at constant volume, but an increase in membrane area results in hemolysis. A theoretical geometric parameter, the "minimum cylindrical diameter" (MCDiam), in microns, the thinnest cylindrical channel through which each individual cell could pass, predicts the linear boundary of the plot of area vs. volume. The MCDiam value of 3.66 µ ± 0.04 SEM accurately represents the thinnest channel through which 95% of the cells can pass.

In two splenectomized patients with hereditary spherocytosis the MCDiam was increased to approximately 4.0 µ, suggesting that the severest restriction is located in the spleen.