k + channel
DESCRIPTION
K + Channel. Sukhee Cho Greg Richard. K+ Channels. Found everywhere Contribute to resting potential (neurons) Major roles in cardiac tissue Involved in hormone secretion. Open. Closed. Slow to close. Inactivated. K + Channel Anatomy. Senyon Choe (2002). Gating. Bezanilla 2004. - PowerPoint PPT PresentationTRANSCRIPT
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K+ Channel
Sukhee ChoGreg Richard
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K+ Channels
• Found everywhere
• Contribute to resting potential (neurons)
• Major roles in cardiac tissue
• Involved in hormone secretion
ClosedOpen
Slow to close Inactivated
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K+ Channel Anatomy
Senyon Choe (2002)
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Gating
Bezanilla 2004
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Classes
• Inwardly Rectifying– ROMK, GIRK, ATP-sensitive
• Tandem Pore Domain– TWIK, TREK, TASK, TALK, THIK, TRESK
• Voltage-Gated– hERG, KvLQT1
• Calcium Activated– BK, IK, SK
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Inwardly Rectifying (Kir, IRK)
• Subclasses: ROMK, GIRK, ATP-sensitive
• 2 TMD, 1 P
• Current flow into cell (“inward”)
• Differ from delayed rectifier or A- type channels (outward current)
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Tandem Pore Domain (K2P)
• Subclasses: TWIK, TREK, TASK, TALK, THIK, TRESK
• 4 TMD, 2 P (two 2 TMD, 1 P)
• “Leak channels” – contribute to resting potential
• Activated by mechanical stretch, pH, temperature
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Voltage-Gated (Kv)
• Subclasses: hERG, KvLQT1
• 6 TMD, 1 P
• Sensitive to voltage changes– S4 domain
• Return to resting state– Repolarization– Limits AP frequency (RRP)
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Calcium Activated (KCa1 )• Subclasses: BK, IK, SK
• 6 TMD, 1 P
• Activated by intracellular Ca2+
• Some activated by intracellular Na+ & Cl-
• N-terminus extracellularly (Unlike Kv)
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Paper #1
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Amyloid β Hypothesis in Alzheimer’s disease
http://en.wikipedia.org/wiki/Beta_amyloid
Alzheimer's diseased brain
Aβ1-40
Aβ1-42
Aβ1-40
Aβ1-42
Amyloid precursor protein
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Controlling neurotransmitter releaseFast after-hyperpolarizationSpike frequency adaptation
VSD - voltage sensing domainPGD - pore-gating domainRCK - regulator of K conductance
Lee et al., Trends Neurosci. 2010 Sep;33(9):415-23. Review.
BK channelLarge conductance Ca2+-activated K+ channels, Maxi-K, BK or Bkca, Kca1.1
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Figure 1. Intracellular infusion of Aβ1-42 broadens spike width and augmemted Ca2+ influx in rat neocortical pyramidal neurons.
Aβ1-40
Aβ1-42
Fura-2
100-250 pA500 ms
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Figure 3. Intracellular Aβ1-42 enlarges spike width by suppressing BK channels, thereby increasing spike-induced Ca2+ entry.
Charybdotoxin - Ca2+-activated K+ channel blocker4-AP(4-Aminopyridine) – A-type potassium channel blocker
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Figure 5. ECS blocked Aβ1-42-mediated suppression of BK channels in rat neocortical neurons.
Isopimaric acid
Electroconvulsive shock
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Figure 7. Blocking effects of ECS on Aβ1-42 was absent in H1aKO mice.
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Figure 8. Spike broadening in 3xTG neurons.
JuvenileJuvenile
4 months of age
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Figure 9. Recovery of single BK current by ECS in 3xTG mice.
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Conclusions
Intracellular Aβ1-42 broadens spike width in neocortical pyramidal neurons by downregulation of BK channel activities.
ECS counteracts Aβ1-42 induced BK channel inhibition by expression of Homer 1a
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Paper #2
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Trek Channels
• Two-pore domain K+ channels (K2P)– 4 TMD, 2 pore
• Subfamilies:– Trek1 (Kcnk2)– Trek2 (Kcnk10)
• Underlie “leak” and background K+ conductances
• Sensitive to membrane stretch, temperature, & pH
• Inhibited by PKC & PKA
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Trek2
• Trek2b– Differs from Trek2a & Trek2c at N-terminus
• Trek2-1p– C-terminal truncation (2 TMD & 1 pore)
Does alternative splicing of Trek2 contribute to functional diversity of channel as seen with Trek1?
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Trek2b
N-terminus
Trek2-1p
C-terminus
Trek2 Variants
Trek2
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Immunoblotting
Myc-tag : N-EQKLISEEDL-C (1202 Da)
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Whole-cell Currents(Voltage-step)
-100mV
+60mV
20mV
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Reversal Potential (Erev)(Voltage-ramp)
-100mV
+60mV
1 s
Non-selective channel
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Whole-cell Currents
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Surface Trek2 Expression
Total Protein
Surface Protein
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Conclusions
• Trek2b exhibited larger currents than Trek2b & 2c; > # of Trek2b channels on membrane surface.
• As [K+]o , Erev ; overexpression of K+-selective channels
• Trek2-1p may require additional assembly to form functional channels.
• N-terminal variation can influence current amplitude and surface level of Trek2 channels, as seen in Trek2b.
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How does nature accomplish high conduction rates and high selectivity at the same time?
Sculpture by Julian Voss-Andreae
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Roderick MacKinnon - 2003 Nobel Prize in Chemistry
Visualize a K+ channel and its selectivity filter
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The signature sequence of the potassium channel
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Yellow : carbon, Red : oxygen
Carbonyl oxygens attract K+ ions
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Yellow : carbon, Blue : nitrogen, Red : oxygen
Electrostatic repulsion favors high conduction rates
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Paper #3
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http://radiographics.rsna.org
The renin-angiotensin-aldosterone system regulating blood pressure
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The angiotensin-renin-aldosterone system regulating blood pressure
Adrenal glomerulosa cells in the zonaglomerulosa
Choi et al., Science
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Aldosterone-producing adenomas (Aka Conn’s syndrome)
One of the most common types of the primary aldosteronism (the overproduction of aldosterone)Conn’s sydrome is caused by a discrete benign tumor of the adrenal gland (APA)Diagnosed between ages 30 and 70Most of them are classified as idiopathic and a small number have mutationsResulting in hypertension and hypokalemia (low plasma K+ level)Surgical procedure can relieve symptoms
Hereditary hypertension
Mendelian form of primary aldosteronismBilateral adrenal hyperplasia (increase in number of cells/proliferation of cells)Bilateral adrenalectomy in childhood
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Protein-changing somatic mutations in aldosterone-producing adenomas
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Mutations in KCNJ5 in aldosterone-producing adenoma and inherited aldosteronism
The probability of seeing either of two somatic mutations recur by chance in 6 of 20 other tumors is <10-30
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H.s., Homo sapiens Human
M.m., Mus musculus Rodent
G.g., Gallus gallus Chicken
X.t., Xenopus tropicalis Frog
D.r., Danio rerio Zebrafish
C.I., Ciona intestinalis Sea squirt
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KCNJ5 channelKir3.4, GIRK4
Subclasses: ROMK, GPCR, ATP-sensitive2 TMD, 1 PCurrent flow into cell (“inward”)Differ from delayed rectifier or A-type channels (outward current)Magnesium ions, that plug the channel pore at positive potentials, resulting in a decrease in outward currents.A voltage-dependent block by external Cs+ and Ba2+
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Location of human mutations in KCNJ5 mapped onto the crystal structure of chicken K+ channel KCNJ12
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KCNJ5 mutations result in loss of channel selectivity and membrane depolarization
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KCNJ5 mutations result in loss of channel selectivity and membrane depolarization
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Membrane depolarization by either elevation of extracellular K+ or closure of K+ channels by angiotesin II activates voltage-gated Ca2+ channels, increasing intraceullular Ca2+ level.
Channel containing KCNJ5 wit G151R, T158A, or L168R mutations conduct Na+, resulting in Na+ entry, chronic depolarization, constitutive aldosterone production, and cell proliferation.