According to West, Todd, Mason, and Bruggen (1966), erythrocytes or red blood cells (RBC’s) are a-nucleated biconcave disc-like cells ranging in diameter from 6 to 9 µm (average = 7.5 µm). The thickness of the RBCs is ca. 1 µm in the center and ca. 2 to 2.4 µm in the peripheral part. In blood, an average of 1012 RBCs is present. Hemoglobin, a haem-protein is comprised of four globin peptide chains, is intimately held within stroma meshwork in RBCs. Its function is to transport O2 from lungs with high pO2 to all the tissues having low pO2. In the presence of CO2 in the tissues, the acidity increases resulting in the release of O2 and consequently protonated hemoglobin caries bicarbonate ion to be release in lungs.
According to Scott (1993), when RBC’s are placed in isotonic solution having the same non-penetrating solute and solvent concentrations to that of cytoplasm, the cell volume does not changed, though water and solute freely move in and out. Upon placing in hypotonic solution (solute concentration is less than inside), water will enter and the cells would swell and hemolyse. In hypertonic solutions (solute concentration more than inside), cells would rapidly shrink and crenate. Osmotic strength of RBC can be judged by either, measuring that concentration of solute which hemolyse and/or recording the hemolysis time. In hypotonic solutions non-electrolytes (sugars) and electrolytes (NaCl, Na+, Cl-) at relatively higher concentrations would hemolyse RBC’s.
Animal RBC’s have directly or indirectly been used in medical science. While most mammalian RBC’s are rich in K+, adult dogs exhibit greater Na+ concentrations. This attribute has implications in Na+/K+ antiport (transport) and Na+/K+- ATPase investigations, particularly under varying tonicity (Parker, 1973). Another vital investigation was on RBC agglutination in response to pathogenic viruses like Rubella, for which animal models were used to mimic the human blood (Ponzi, Pugliese and Peutusio, 1978). Recently, animal RBC’s were tested as “artificial” or “universal” blood to be used for human transfusion.
In normal course, animal blood would be rejected by human because of incompatibility of ABO- and D type antigen-antibody. It is now possible to immuno-camouflage the unmatched RBC surface antigens by shielding the cells with methoxy polyethylene glycol (MPEG). Such coating enables masking of surface antigens, without any effect on osmotic and O2 binding capabilities of the RBC’s (Lublin, 2000; Tan et al., 2006).
In such transfusions, another problem that may be faced is differential tonicity of the serum. Optimally, those RBC’s which withstand the lowest hypotonic strengths would be the most suitable system for human transfusion. Hemolysis time at 0.3 M glycerol + 0.12% NaCl is the highest (850 seconds) among mammals tested (Scott, 1993), which means that the membrane can withstand higher turgidity than the others.
The hemolytic behavior of given RBC’s, representing the intactness of the membrane, was tested using graded concentrations of NaCl with one control without the salt. The blood was mixed and after an incubation of 37oC and centrifuged. The release of hemoglobin (pink color), read by a colorimeter, represents hemolysis and no deposit (pellet), and the cells that shrunk but remained intact did not release hemoglobin and precipitated like normal cells do.
In control, pink color and no deposit indicated that hemolysis took place as expected because the solution was indeed hypotonic. Up to O.6% NaCl, the same phenomenon was seen (% hemolysis = 89.5±6.5). At 0.7% concentration also there was partial release of hemoglobin, could be due to the permeability barrier not accounting for hemolysis. However, concentrations > 0.7% exhibited negligible hemolysis and deposition of shrunken cells. Hence, ca. 7% NaCl (1.23 M) appears to be isotonic, < 7% hypo- and > 7% hypertonic solutions for the given RBC’s.
References
West, Edward S., Wilbert R. Todd, Howard S. Mason, and John T.V. Bruggen. Textbook of Biochemistry (4th Ed.). New York: Macmillan Publishing Co. Inc., 1966.
Scott, Linda, A. “Diffusion across a sheep red blood cell membrane.” Tested studies for Laboratory teaching, vol. 14 (Goldman, C.A. Ed.). Association of Biology Laboratory Education. Web.
Parker, John C. “Dog red blood cells: Adjustment of salt and water content in vitro.” The Journal of General Physiology 62 (1973): 147-156. Web.
Ponzi, Alessandro N., Agostino Pugliese, and Patrizia Peutusio. “Rubella virus hemagglutination with human and animal erythrocytes: Effect of age and trypsinization.” Journal of Clinical Microbiology 7 (5) (1978): 442-447. Web.
Lublin, Douglas M. “Universal RBCs.” Transfusion 40 (2000): 1285-1289. Web.
Tan, Yingxia, Yan Qiu, Hua Xu, Shouping Ji, Subo Li, Feng Gong, and Yangpei Zhang. “Decreased immunorejection in unmatched blood transfusions by attachment of methoxy polyethylene glycol on human red blood cells and the effect on D antigen.” Transfusion 46 (2006): 2122-2127. Web.