transfusion red cell membrane part 1 of 1 week 2.pdf

Geoff White (from Moore, Knight & Blann,2010) 1 Session Aims and Outcomes this session aims for you to gain an understanding of :  the Red Cell Membrane and its Constituents  function of the Red Cell Membrane  How structure of red cell membrane allows...

Geoff White (from Moore, Knight & Blann,2010) 1 Session Aims and Outcomes this session aims for you to gain an understanding of :  the Red Cell Membrane and its Constituents  function of the Red Cell Membrane  How structure of red cell membrane allows it to perform its function By the end of this session you should be able to explain:  How the red blood cells membrane and constituents work together  How the membrane works to maximise red cell lifespan  How the structure of the membrane relates to its function.  Red Blood Cells  ‘erythrocytes’ have a bi-concave disc shape  their role is to  transport respiratory gases to/from tissues  deliver oxygen (O2) to the tissues where active metabolism is going on  to remove the waste products of metabolism from the tissues  Red Cell Facts  on average a healthy adult male has 5,000,000,000,000 in each litre of blood  they develop in the bone marrow but lose their nucleus by the time they reach the bloodstream  contain Haemoglobin which enables oxygen delivery to the tissues  average life-span of 120 days in the blood circulation  reduced life-span can lead to haemolytic anaemia  Function of Red Cell Membrane  function in microcirculation means red cell membrane must be tough but flexible and show deformability  achieved by interaction of a protein cytoskeleton with the membrane lipid bilayer  main functions  separate the cell contents from the plasma  maintain characteristic shape  regulate intracellular cat ion concentrations  site of membrane surface receptors  The Red Cell Membrane composed of  an outer Glycocalyx carbohydrate ‘coat’ made up of both extracellular proteins and glycosylated proteins & lipids from the Lipid Bilayer  underneath is the framework of peripheral proteins that comprise the red cell Cytoskeleton Chemical structure  44% lipid  acts as permeability barrier  comprise a basic phospholipid bilayer  49% protein  integral or peripheral  provide skeletal structure and selective transport across membrane  7% carbohydrate  associated with proteins/polypeptides or lipid (ie glycosylated)  presented on the outside of the membrane  The Red Cell Membrane  Red Cell Membrane showing Glycocalyx, Lipid Bilayer & Cytoskeleton (from Issitt & Anstee,1999)  Composition of the Red Cell Membrane  Membrane Lipids  30% cholesterol  60% Phospholipid  Phosphatidyl choline (lecithin)  Sphingomyelin  Phosphatidyl ethanolamine  Phosphatidyl serine  characterised by polar head group attached to a non- polar fatty tail  arranged in a bilayer  fluidity allows movement of ‘rafts’  10% glycerides/FFA Composition of the Red Cell Membrane Integral Proteins  Band 3  facilitates anion transport across the membrane  binding site for skeletal and other red cell proteins  has binding sites for Hb, ankyrin, Band 4.1, Band 4.2  Glycophorins (A,B,C,D,E)  Sialoglycoproteins provide negative charge  act as binding sites for viruses, bacteria, parasites  required for structural integrity of the red cell  Glucose Transport Protein  12 trans-membrane domains  surface concentration varies  Rh Proteins  associated into a macrocomplex  transport function & interacts with cytoskeleton  Peripheral Proteins of the Cytoskeleton  membrane peripheral proteins interact to form the cytoskeleton Peripheral Proteins are  Spectrin  subunits bind in an anti-parallel arrangement  associates with Ankyrin, band 4.1, actin & anionic phospholipids  Ankyrin  found in 2 forms  anchors spectrin molecules to the lipid bilayer  Actin  globular protein that polymerises readily to form filaments  bind weakly to the tail end of spectrin and holds together in a 2D lattice  Band 4.1  globular protein that binds to spectrin close to the actin binding site  binds directly to glycophorins A & C, Band 3, phosphatidyl serine & ankyrin  Peripheral Proteins of the Cytoskeleton  membrane peripheral proteins interact to form the cytoskeleton Peripheral Proteins are  Spectrin  subunits bind in an anti-parallel arrangement  associates with Ankyrin, band 4.1, actin & anionic phospholipids  Ankyrin  found in 2 forms  anchors spectrin molecules to the lipid bilayer  Actin  globular protein that polymerises readily to form filaments  bind weakly to the tail end of spectrin and holds together in a 2D lattice  Band 4.1  globular protein that binds to spectrin close to the actin binding site  binds directly to glycophorins A & C, Band 3, phosphatidyl serine & ankyrin  Peripheral Proteins of the Cytoskeleton  membrane peripheral proteins interact to form the cytoskeleton Peripheral Proteins are  Spectrin  subunits bind in an anti-parallel arrangement  associates with Ankyrin, band 4.1, actin & anionic phospholipids  Ankyrin  found in 2 forms  anchors spectrin molecules to the lipid bilayer  Actin  globular protein that polymerises readily to form filaments  bind weakly to the tail end of spectrin and holds together in a 2D lattice  Band 4.1  globular protein that binds to spectrin close to the actin binding site  binds directly to glycophorins A & C, Band 3, phosphatidyl serine & ankyrin Integral Proteins  Glucose Transport Protein (GLUT 1)  Glycophorin A  Red Cell Na+/K+ ATPase ‘ cation pump’  enzyme composed of 3 protein subunits  catalyses the conversion of ATP to ADP to release energy  ADP formed is reconverted to ATP by the EM Pathway  each ATP hydrolysed removes 3 Na+ molecules and subsequently transports 2 K+ into the cell  Mechanism of Na+/K+ ATPase ‘pump’  Phosphorylation (energy release) of the pump transports out 3 NA+ molecules  Dephosphorylation transports 2K+ into the cell  Peripheral Proteins of the Cytoskeleton  membrane peripheral proteins interact to form the cytoskeleton Peripheral Proteins are  Spectrin  subunits bind in an anti-parallel arrangement  associates with Ankyrin, band 4.1, actin & anionic phospholipids  Ankyrin  found in 2 forms  anchors spectrin molecules to the lipid bilayer  Actin  globular protein that polymerises readily to form filaments  bind weakly to the tail end of spectrin and holds together in a 2D lattice  Band 4.1  globular protein that binds to spectrin close to the actin binding site  binds directly to glycophorins A & C, Band 3, phosphatidyl serine & ankyrin Representation of Membrane Structure Primary Membrane Disorders  inherited disorders of the red cell membrane  affects cell shape  reduced life-span can lead to compensated anaemia  Hereditary Spherocytosis  autosomal inheritance  results in defective/deficiency of skeletal proteins  mainly affects spectrin  causes spherocytosis & haemolytic anaemia Primary Membrane Disorders  Hereditary Elliptocytosis  presence of a large proportion of oval or elliptical cells  defective spectrin, Band 4.1, or Band 3   Rh Null Syndrome  absence of Rh Polypeptides and RhAG in membrane  stomatocytosis & spherocytosis observed in peripheral blood  patient experiences compensated haemolytic anaemia