Ion channels; Thermo-TRP Flashcards
List the key features of TRPV1 ion channels. Refer to structure, expression & regulation
Expression (300-WL) (1) (1/4)
Small- to medium- diameter primary sensory neurones
with soma in the DRG, trigeminal and nodose ganglia
List the key features of TRPV1 ion channels. Refer to structure, expression & regulation
Structure (300-WL) (1) (2/4)
- Homo-tetramers
- Structure resembles that of a VGIC
- Ion permeation pathway formed by TM helices S5/6 & the intervening loop region
- 6 TM domains & a short pore-forming h-phobic stretch b/w 5th & 6th TM domains
List the key features of TRPV1 ion channels. Refer to structure, expression & regulation
Activation (300-WL) (1) (3/4)
- Temp threshold can be reduced by action of pro-inflam mediators (released during T injury/inflam)
- Activators:
- Vanilloids (capsaicin)
- > 40°C
- non-selective cation receptors
- gated by array of noxious ligands
List the key features of TRPV1 ion channels. Refer to structure, expression & regulation
Regulation (300-WL) (1) (4/4)
- Gated by noxious heat, protons, voltage & memb-lipids
- Polymodal regulation
- makes them v versatile & = important for their role in sensing (burning) pain
- 1 type of desensitisation = tachyphylaxis:
- reduced TRPV1 responses to repetitive stimuli
- intensity of tachyphylaxis = reg by strength of inducing stimulation
- TRPV1 channels undergo an activity-gated recycling to reg their surface XPS’ion lvl
List the key features of the P2Y receptor family
Expression (300-WL) (2) (1/4)
- present in almost all human T
- present in bone cells (suggestive of involvement in bone physiology & pathology)
- located on cell membranes
List the key features of the P2Y receptor family
Structure (300-WL) (2) (2/4)
- family of purinergic class A GPCRs (7-TM)
- 8 P2Y receptors cloned in humans
- 2 subgroups based on struct similarities
- P2Y1-like GPCRs
- P2Y12-like GPCRs
- Endogenous agonists: ATP/ADP/UDP/UDPG
- couple to different G-proteins (P2Y12-like all Gi & P2Y1-like = Gq, Gi, Gs)
- signalling via diverse G-proteins to activate/inhibit diff pathways
- 7 h-phobic TM helices
- connected by 3 short extracellular loops & 3 variably sized intracellular loops
- extracellular = ligand
- intracellular activate G-protein, control receptor internalisation & mediate dimerisation
- both homo- & heterodimers
- 4x extracellular Cys, form 2x S-S
- N-T @ proximal extracellular loops
- b/w the two remaining extracellular loops
- S-S involved in ligand binding
- @ C-T = protein kinase binding motif
- influences degree of P2Y subtypes coupling to Gq, Ga, Gs, Gi proteins via intracellular loop structural diversity
List the key features of the P2Y receptor family
Activation (300-WL) (2) (3/4)
- extracellular nucleotides (ATP, ADP, UTP, UDP, UDP-Glucose) in extracellular milieu
- response can be +/-
- individual P2Y-R may respond to only purine/ pyrimidines/ both
- activity = linked to signalling cascades rooted within the flow of Ca and K ions by the R’s interactions with different G-proteins
- this modulates access to Ca & K ion channels
List the key features of the P2Y receptor family
Regulation (300-WL) (2) (4/4)
- mediate responses inc. vasodilation, blood clotting, IR (phago, antigen-presentation, chemotaxis, degranulation, cytokine production, lymphocyte action)
- Ubiquity & variety of funct means = common targets of pharmacological development of drugs
- specific subtypes can be internalised by adenosine derivatives i.e., adenosine 5’-O-1-boranotriphosphate (ATP-α-B) induces internalisation of P2Y_1 and P2Y_2 receptors
- this was discovered by using using HEK293 cells expressing rat P2Y_1 and P2Y_2 receptors attached to GFP
- agonist-induced receptor endocytosis: [Ca] rise & arachidonic acid release
Discuss the role of TRP ion channels in the sensation of temperature in the human body (1500-WL)
Introduce TRP ion channels & summarise their roles - TRP ion channels (permeation; families; activators; TRPV1) (3) (1/9)
- cation-permeable channels
- 28 molecules, 6 sub-families (sequence homology)
- diff receptors = activated by diff temp ranges (nociceptors; temp-sensitive) & exposure to natural stimuli (capsaicin; TRPV1)
- TRPV1 (peripheral sensory neurones) = mostly resp for pain sensation caused by stimuli (noxious heat, elevated [H+], vanilloid compounds)
- Activation → integration of signals via inherent ion conductance properties → kinase activity
- allow organism to detect ambient enviro, search for favourable conditions & avoid harm
- have roles @ cellular lvl (neurite growth, vaso-dilation/constriction)
Discuss the role of TRP ion channels in the sensation of temperature in the human body (1500-WL)
Introduce TRP ion channels & summarise their roles - Thermosensation (temp-dep; Q10) (3) (2/9)
- Gating of some TRP channels have steep temperature-dependencies within physiological temp range (36.1°C - 37.2°C)
- have roles in thermosensation, -regulation & metabolism
- channels characterised according to temp co-efficient, Q10 value
- ∆ in current amplitude upon a temperature ↑ of 10 °C
- characterises temp sensitivity of a channel
-Q10 dictates that:- TRPV1-4 = warm sensitive
- TRPM8 = cold sensitive
- temp sensitivity alone ≠ sufficient enough to infer that these channels are functionally relevant temperature detectors
- also need to be:
- XPS’d in physiologically relevant locations that can detect temp ∆’s
- functionally characterised by their thermosensory phenotypes in genetically tractable organisms (KO mice, mutant drosophila/c. elegans)
Discuss the role of TRP ion channels in the sensation of temperature in the human body (1500-WL)
Introduce TRP ion channels & summarise their roles - General roles (excitable; non-excitable) (3) (3/9)
- plethora of roles observed by these channels
- participate in many physiologically relevant processes in the diff cells & T they are XPS’ed in
Excitable cells
- TRP channels mediate flux of Na & Ca across PM into cytoplasm → depolarisation & AP → NTM release
Non-excitable cells
- Depolarisation stimulates voltage-dep channels (Ca, K, Cl) → influences cellular events (TC, TL, contraction, migration)
Discuss the role of TRP ion channels in the sensation of temperature in the human body (1500-WL)
Introduce TRP ion channels & summarise their roles - Difficulty in studying (limited understanding; relevant locations) (3) (4/9)
- understanding has been limited by criteria (expression & tractable organisms), so relevance called into question
- knowing their XPS’ion can help tackle roles of these channels
- can be expressed on animal PM
- neurones innervating skin = most likely to experience largest temp Δ’s
- smaller temp Δ’s occur within body cavity, intestines, CNS & other T
- can be expressed on animal PM
- latter temp Δ’s are more clearly physiologically (& ≈ pathologically) relevant bc they ≈ be monitored by sensory mech
- limited knowledge of molecular markers for the channels → interoceptive temp channels remain elusive
Discuss the role of TRP ion channels in the sensation of temperature in the human body (1500-WL)
Mitochondrial biogenesis TRPV1 (3) (5/9)
- TRPV1 (vanilloid superfam) opens when temp = ≥ 40°C under norm cond
- homologs = heat-activated, distinct temp thresholds
- Temp sensing is imp in mito biogenesis (MB)
- Skeletal muscle cells: High °C = activate TRPV1 (longitudinal sarco ret)
- induces Ca release from SR → cyto
- ↑ cyto [Ca] → activation of RyR1 (Ca gatekeeper in muscle cells on SR) → more SR Ca release
- LT TRPV1 activation ≈ promote MB
- ≈ via the Ca-CaMKII-p38 MAPK-PGC-1α signalling axis (@ bottom)
- maintaining intracellular Ca homeostasis = essential for cellular function (exercise: muscle cells reach 37-42°C)
- relevance: may improve endurance & E metabolism
- impaired aerobic exercise capacity & skeletal muscle dysfunction = ass w/ cardiometabolic diseases
Ca-CaMKII-p38 MAPK-PGC-1α signalling axis
- intracellular Ca induces the CaMKII cascade
- 1) activates AMPK → +p to PGC-1α
- 2) carries on downstream, inducing p38 MAPK cascade → activates PGC-1α
Activated PGC-1α → increases TC of nuclear-encoded mito genes & induces TFAM translocation to mito to induce TC of mito-encoded mito genes
Discuss the role of TRP ion channels in the sensation of temperature in the human body (1500-WL)
Mitochondrial biogenesis Specific examples (TRPV1 expression & PGC-1α levels; C2C12; meta-analysis) (3) (6/9)
1)
Observed:
- expression of TRPV1 & cyto[Ca] (skeletal muscle cells) ↑’ed when mice were fed with capsaicin (4mths)
- ↑ XPS’ion of PGC-1α (regulator of MB)
- enhanced aerobic endurance capacity
2)
Investigated physiological relevance (TRPV1) in MB during exercise
- C2C12 myotubes (cell line: form contractile myotubes & produce characteristic muscle prot) exposed to capsaicin had an ↑ cyto[Ca] & XPS’ion of PGC-1α
- ✓ in vivo: PGC-1α upregulated in mice skeletal muscle cells (TRPV1+capsaicin OR over-XPS’d)
- XPS’ion of genes ass with fatty acid ox & mito respiration = ↑
- MB & endurance ↑
- absent when TRPV1 KO mice used
- conclusion: TRPV1 has physiologically relevant role in sensing temp rises during exercise
- reg & induces MB as a mech to maintain cellular homeostasis
3)
meta-analysis
- revealed no differences b/w capsaicin & placebo activation of TRPV1
- b/ a ergogenic effect (↑) was obsv for muscular endurance
- sig pathways must integrate and ↑ XPS’ion of MB-related genes, not just TRPV1 involved - questions relevance again
Discuss the role of TRP ion channels in the sensation of temperature in the human body (1500-WL)
Immune response TRPV1 in IL6 response (3) (7/9)
- TRPV1 = integrator of noxious chemical & physical stim (→ irritation & pain)
- activation ≈ linked to acute nociceptive pain & neurogenic inflam
- ≈ IL6 released from skeletal muscles ≈ induced by TRPV1 activation (heat) → signal into nucleus → induces prod of IL6
- ↑ IL6 carries out immune & metabolic processes in muscle cells (anti-/pro-inflam)
