Lecture 6-10 Flashcards
How is the resting membrane potential regulated?
by the movement of potassium ions in and out of the cell
What are the key stages of an action potential?
- Resting phase
- Depolarisation
-> slow rising phase
-> rapid rising phase - Repolarisation
- Hyperpolarisation (refractory period)
What occurs in depolarisation?
sodium channels open = influx of sodium into the membrane (fast) = membrane potential becomes more positive
What occurs in repolarisation?
- potassium channels open
- passive efflux of potassium out of the membrane (slow)
- membrane potential becomes more negative
What occurs in the refractory period?
- sodium channel and potassium channels close
- Na+ and K+ pump open
- resting membrane potential is restored
How does an action potential travel down an axon?
-Travel down an axon via current loops. Refractory period prevent the action potential from going backwards
What is the mode of action of Tetrodotoxin (TTX)?
sodium channel inhibitor (blocks the pore)
What section of the action potential graph would be impacted by TTX?
depolarisation
What is channelopathies?
pathology/disease arising from ion channel dysfunciton
What is the difference between autosomal dominant and autosomal recessive?
autosomal dominant = carrier and has the gene
autosomal recessive = one affected allele
What are the main types of ion channel pain mechanisms?
- Nociceptive = sensing in the periphery e.g temp
- Inflammatory = inflamed molecules drive pain
- Neuropathic = pain due to damage received inside the nervous system
How does nociceptive pain work in regard to ion channels?
temperature related ion channels with mechanical release ion gated ion channels
How does inflammatory pain work in regard to ion channels?
various immune cells with granules like histamine can trigger pain responses
How does neuropathic pain work in regard to ion channels?
arise from damage to the nervous system which changes expression in ion channels and post-translational modification of nociceptors.
What are the 4 potential therapeutic strategies for pain?
- inhibit the ion channel that sens the stimuli and initiates the action potential
- inhibit the ion channel that propagate the action potential = receive the signal but block the signal from traveling up the axon
- inhibit the ion channel involved in DRG neurotransmission = block the ion channel at the synapse from the peripheral nervous system to the central nervous system
- inhibit the ion channel that process the stimuli centrally within the brain
What is primary erythromelalgia (PEM)?
mutations in SCN9A (autosomal dominant) which causes episodes of burning pain in feet and hands, attacks triggered by exercise and/or heat.
What is Paroxysmal extreme pain disorder?
mutation in SCN9A (autosomal dominant), severe pain in the rectal, ocular and mandibular and attacks triggered by chewing and/or heat.
What does mutations result in Paroxysmal extreme pain disorder?
Mutations result in incomplete channel inactivation and sustained excitability = not able to activate the action potential because its is constant excitability.
What is SCN9A refered to as?
the pain gene
What are the 4 major types of animal tissues?
- epithelial
- musclar
- nervous
- connective
What is the difference between connective tissue and epithelial/muscular/nervous?
- connective tissue = has less cells per area and move in extracellular space
- epithelial/muscular/nervous tissue = compact with cells and have very little extracellular space
What is the function of epithelial cells?
form cell junctions which allow them to link with each other to form a rigid structure.
How do cells contact each other in tissue?
produce cell junctions to interact with neighbouring molecules and cells
What are the 4 types of cell junctions found in epitherlial tissue?
- Cadherin
- Desmosomes
- Tight junctions
- Gap junctions
What are cadherin and what is their role?
- superfamily of Ca2+ dependent molecule
- transmembrane-spanning molecule with two extracellular domains that are important for holding the cells together by binding one actin for one cell to the actin in the other cell.
What is the role of calcium in cadherins?
- ca2+ binding prevent flexing = promotes homophilic binding to another cadherin
- molecule is flexible until calcium is added so the molecule becomes rigid.
How do intracellular domains of cadherins interact with actin?
- via catenins and other adapter proteins
- contain sequences which allow for the docking of catenins which associate with the intercellular domain.
What is the function of Desmosomes?
- contain specialized cadherins that connect with intermediate filaments = allows cell junctions to withstand mechanical force
What is the function of Tight junctions?
- form a selective permeability barrier
- make sure molecules in the lumen don’t leak through the cell
What proteins hold the tight junction together?
Claudin and occludin
What is the function of Gap junctions?
- allow small molecules to cross from one cell to another by forming small channels
What are the gap junction channels made of?
made from connexins and innexins
What are the different functions of the extracellular matrix?
Provides..
- support and strength
- cellular communication
- cell migration, polarity and shape
What is the basal lamina?
a very thin layer of extracellular matrix produced by cells above and below
What is the basal lamina composed of (other than ECM)?
- laminin
- type IV collagen
- type XVIII collagen
- nidogen
- perlecan fibronectin
What is the role of ECM in connective tissue?
ECM is the main stress-bearing component of connective tissue and forms an indirect form of cell-cell contact
What are the other cells in connective tissues and what are their functions?
- PRIMITIVE MESENCHYMAL CELLS = undifferentiated cells that lead to generation of other connective tissue cells
- FIBROBLASTS = synthesize molecules found in ECM
- SPECIALIZED CELL (e.g adipocytes, mast cells, chondrocytes) = found in specialized connective tissue e.g cartilage and bone
- CHONDROCYTES, OSTEOBLASTS = make up the cartilage matrix
What are the features of connective tissue ECM?
- high molecular weight = highly charged polysaccharides covalently attached to proteins that bind lots of water
- fibrous proteins (member of collagen family
- glycoproteins
What is a GAG and what is its role in the ECM?
- GAG = consists of repeating sulphated disaccharide units
- linked to a core protein to form proteoglycans
What is the role of Aggrecan?
GAGs bind onto aggrecan
- aggrecan can aggregate with other aggrecan molecules and bind to hyaluronan
What is the structure and role of collagen?
- 3 polypeptides form a coil which can self-aggregate into fibrils and fibers
- prevents aggregation from happening inside cells
What is the function of elastins and fibronectins?
- ELASTINS = provide elasticity to connective tissues (dominant component of ECM found in arteries)
- FIBRONECTINS = bind other matrix/cell membrane proteins so they can communicate
What is the role and structure of integrins?
integrin = receptor that binds ECM components
structure:
- alpha and beta chain with large N terminal domain
- short intracellular domain that binds adapters similar to those seen with cadherins
- talin = important adapter molecule
What is the role of an active integrin?
- allows the cell to contact the matrix protein kinetically so cells can pull themselves through the matrix
Why do integrins need an “inactive” conformation?
cells in connective tissue are not stationary and migrate through ECM, cell-ECM contacts need to be made and broken to move the cells.
How does activation of integrins work?
- cell has receptor which will recognize pieces of the matrix -> leads to signaling pathway in the cell -> alters integrin shape to open them up
What is the extracellular matrix?
a network of fibrous proteins and hydrated proteoglycans which surround cells in tissues.
How is a healthy ECM maintained?
cells with ECM secrete the components of ECM = secrete enzymes which digest/breakdown these components to remove damaged matrix
Why does ECM component need to be broken down?
to counterbalance ECM synthesis to maintain a healthy matrix
What is the function of the degradome?
degrading other products in the genome
What are the 3 minimal domains of the metalloproteinase enzymes?
- MMP (matrix metalloproteinases)
- ADAM (a disintegrin-like and metalloproteinase)
- ADAMTS ( a ADAM with thrombospondin motifs)
What is the function of each of the 3 minimal domains of the metalloproteinase enzymes?
- MMP = key ECM modifiers
- ADAM = membrane-bound enzymes
- ADAMTS = secreted into ECM like MMPs and involved in ECM breakdown
What are the metalloproteinase enzymes characterised by?
- Zn2+ binding catalytic domain
- secretion into ECM as inactive pro-enzymes
- activated by removal of pro “bait” region by other proteinases
- high degree of specificity
What are the metalloproteinases inhibited by?
- alpha2 macroglobulin
- tissue inhibitors of metalloproteinases (TIMPs) which slot into active sites of the catalytic domains
ECM synthesis/breakdown is essential in what other ways?
- embryonic development
- wound healing
- prevention of tumor development
What are the steps for control of metalloproteinase activity?
- enzymes bind through transcription at the front of the cell
- enzymes are released and matured
- enzymes are active and catalyze the matrix
- inhibitor binds to the enzyme to inactivate them and bring them into the cell
- cell degrades the inactivated enzymes
How does recognition of ECM breakdown lead to homeostatic control?
ECM fragments are recognised by integrins expressed by many ECM cells = signaling results in increased ECM synthesis
