The Red Cell Membrane Flashcards
What is the normal arrangement of the phospholipids in the red cell membrane?
Outer membrane: Phosphatidylcholine and sphingomyelin
In the inner layer phosphatidyl ethanolamine and phosphatidylserine
What molecules are important in the maintenance of the membrane?
Flippase
floppase
scramblase
they aim to prevent the exposure of PS to the outer layer
What are the most significant RBC membrane proteins currently known about?
Blood group antigens
Transport proteins such as band 3 RhAG - o2 and co2
AQP1 and glut 1
Adhesive proteins and signalling receptors
What happens if there is exposure of inner proteins to the outer membrane?
This triggers apoptosis and phagocytosis by macrophages
Give examples of adhesive protein?
ICAM4 and Lu
What are the mechanical and functional features of the red cell?
Mechanical: Strong and resistant to damage Elastic and deformable Elongates upto 250% its original dimensions (longitudinal only, otherwise can lyse cell) Functional functions: Ag presentation Molecule transportation maintenance of phospholipid dysequilibrium to evade macrophage phagocytosis
What are some membrane transport proteins?
Band 3 AQ1 Glut1 Kidd antigen protein RhAG Na-K-ATPase Ca ATPase Na-K-2Cl co transporter Na-cl co transporter gardos
What is the function of ankyrin complex?
it anchors the structure onto the spectrin proteins
What is the action of the 4.1R complex?
cellular elongation
binds the duffy antigen and glut 1
What is Spectrin composed of?
alpha and beta
filamentous triple helices of repeats of 106AAs
What do the anchoring proteins bind to?
Actin
Adducting dermatin tropomyosin
How is the biconcave disc maintained in the RBC?
Strong cohesion between the lipid bilayer and skeletal proteins stop membrane vesiculation
The integrity of the membrane is maintained by strong interactions in the skeletal proteins and phospholipids
Cation regulation is also important as maintains RBC volume
What is cytoplasmic viscosity?
Ability of the cell to change shape
What is cytoplasmic viscosity governed by?
Hb conc in the cell MCHC
What do increases in cytoplasmic viscosity lead to?
Increases in viscosity hamper the abilty of the cell to squeeze through microcirculation whcih affects tissue oxygen delivery
What causes a membrane to deform?
Spectrin repeats - more spectrin repeats - more folding and unfolding units
In what diseases is the membrane/skeletal protein mutated?
Hereditary spherocytosis
Hereditary Elliptocytosis
Hereditary stomatocytosis
Hereditary ovalocytosis
What is seen in hereditary spherocytosis?
Autosomal dominant anaemia jaundice reticulocytosis splenomegaly gallstones spherocytes in blood films
What is the cause of the spherocytosis?
Membrane surface area loss occurs due to reduction in loss of cohesion of membrane component due to mutations in the vertical complexes
What is the cause of hereditary elliptocytosis?
AD disease
Loss of CSM SA due to mutations in roteins important in horizontal adhesive proteins
Hereditary stomatocytosis?
high cytoplasmic cation content gives rise to overhydrated cells that look like stomatocytes
Hereditary ovalocytosis?
Single mutation in band 3 - loss of deformability common in SEasians
Quick run down of the structure of the red cell membrane?
Lipid bilayar, with a network of skeletal proteins beneath the inner layer (e.g alpha spectrin)
-The membrane is studded with transmembrane proteins such as Band 3 (transport protein) and ICAM4 (Adhesion proteins`0
-It is highly elastic and deformable
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