THE RED CELL MEMBRANE BLOOD BANKING Prepared by: JOSEPHINE C. MILAN, RMT, MSMT DEPARTMENT OF MEDICAL LABORATORY TECHNOLOGY UNIVERSITY OF TABUK
OBJECTIVE and FOCUS • To correlate the structure of the red cell membrane with the occurrence of blood group antigens and how it is influenced by storage conditions.
RATIONALE • Q: WHY DO WE STUDY THIS TOPIC ? • The main purpose of blood transfusion is to supply red cells which should remain viable and functional in the transfused patient/ recipient. • We have to understand the nature of RC membranes. • Mainly, blood groups antigens are located in /on the red cell membranes. The structure of the red cell membranes has certain roles for its functionality. There are important things to remember about the characteristics of red cell membranes.
TOPIC OUTLINE (based on syllabus) • 1. Red cell membrane structure • 2. Blood group antigens on the red cell membrane • 3. Other properties of the red cell membrane • Main reference: Modern Blood Banking and Transfusion Practices by Denise M. Harmening. F.A. Davis Company. Philadelphia 5thed
RED CELL FUNCTION Main function of red cells: • Totransport oxygen to tissues, and bind carbon dioxide from tissues to be brought to the lungs for excretion. Importantfor RBC survival and function: 1. normal chemical composition and structure of the RBC membrane 2. hemoglobin structure and function 3. RBC metabolism
RED CELL MEMBRANE STRUCTURE RBCMembrane: • 1. RBC membrane is a semipermeable lipid bilayer supported by a protein meshlike cytoskeleton structure. • 2layer of lipids • proteins
RED CELL MEMBRANE STRUCTURE • 2. Behaves as semisolid, with elastic and viscous properties • important and critical for survival in the circulation for 120 days going through numerous cycles and passages through narrow veins and sinusoids in the spleen. • in RBC deformability and permeability (crucial / critical characteristics)
Biochemical structure • 3. The cell membrane consists of : protein, lipids, and carbohydrates • Ratio of- 52 (P) : 40 (L) : 8 (C)
PROTEINS IN THE MEMBRANE Proteins: form a meshwork that traverse the lipid bilayer, calledmembrane skeleton • 2 types of proteins: • a. “integral” membrane proteins-which are in contact with both sides of the membrane; provides anion channels through the RBC membrane • b. “peripheral” proteins – located and limited to the cytoplasmic/inner surface of the membrane forming the RBC cytoskeleton; gives the cell its biconcave structure
jcm 11/2008 Types of membrane PROTEINS
LIPIDS on the membrane • phospholipids = 50 %; cholesterol = 40 %; glycolipids = 10 % • PHOSPHOLIPIDSform a bilayer hydrophobic (nonpolar) tails towards inside of cell hydrophilic (polar) head groups towards outside (extracellular) or the inside (cytoplasmic ) surface • the outer leaflet (external layer) contains electrically neutral glycolipids and choline phospholipids; while • the inner leaflet (internal cytoplasmic layer) predominantly contains phosphatidyl serine which is negatively charged.
CARBOHYDRATES on the membrane • Carbohydrates : forms theglycocalyx, serving as a negatively charged barrier , around the outside of the RBC membrane. • important in preventing cells from adhering(attachment) to one another, or adhering to the endothelium (vein wall)
BLOOD GROUP ANTIGENS on the RC membrane • Majority carried on transmembrane proteins • Few antigens carried on glycosylphosphatidyl -inositol (GPI)- linked proteins or on glycolipids • Some transmembrane proteins interact with other transmembrane proteins Ex: (band 3 and GPA) like Kell and Kx, Rh and RhAG • Some antigens are adsorbed from plasma : Lewis, Chido
PROPERTIES of RC membrane • RBCs are biconcave disks, mean diameter of 7-8 µm • Have more surface area than volume, which creates a soft, pliable cell. • Mature cells have no nucleus or mitochondria, but it is packed with enough metabolism to exist for 120 days.
PROPERTIES of RC membrane DEFORMABILITY • red cell must be easily deformed/change shape • advantageous when these pass through small openings or channels, as in the spleen • Causes of loss of deformability / rigidity of cell : • Loss of ATP decreased phosphorylation of spectrin • Increase deposition of calcium onto cells • examples : spherocytes, “bite cells” • cell become easily lyzed
PERMEABILITY • important to prevent colloidal hemolysis and control the volume of RBC: • favorable toactive cation transport • permeable to water and anions, like chlorides and bicarbonate • relatively impermeable to cations like Na and K • Intracellular : extracellular ratio of Na -1:12; K -25:1 • cationic pump for active transport (requiring ATP) of Na and K .
Ca is transported outward from cell, depends on Ca- ATPase pump • Calmodulin ( calcium-binding protein)- control the ATPase pump; prevent excessive intracellular buildup which leads to rigidity. • When ATP is depleted, Na and Ca accumulate intracellularly, K and water get out of the cell dehydration and rigidity of cell easilysequestered (trapped)in the spleen , thus decrease in RBC survival.