K + Channel Sukhee Cho Greg Richard. K+ Channels Found everywhere Contribute to resting potential...
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Transcript of K + Channel Sukhee Cho Greg Richard. K+ Channels Found everywhere Contribute to resting potential...
K+ Channels
• Found everywhere
• Contribute to resting potential (neurons)
• Major roles in cardiac tissue
• Involved in hormone secretion
ClosedOpen
Slow to close Inactivated
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
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)
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
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)
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)
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
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
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
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
Figure 5. ECS blocked Aβ1-42-mediated suppression of BK channels in rat neocortical neurons.
Isopimaric acid
Electroconvulsive shock
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
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
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?
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.
How does nature accomplish high conduction rates and high selectivity at the same time?
Sculpture by Julian Voss-Andreae
Roderick MacKinnon - 2003 Nobel Prize in Chemistry
Visualize a K+ channel and its selectivity filter
The angiotensin-renin-aldosterone system regulating blood pressure
Adrenal glomerulosa cells in the zonaglomerulosa
Choi et al., Science
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
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
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
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+
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.