Download Voltage-Gated Calcium Channels

Voltage-Gated Calcium
Channels
Daniel Blackman, Zhihui Zhou, Thomas Arnold
Calcium Ion Channel Family
• Cav1 = initiate contraction, secretion, and regulation of gene
expression, integration of synaptic input in neurons, and synaptic
transmission at ribbon synapses of specialized sensory cells
• Cav2 = synaptic transmission of fast synapses
• Cav3 = important for repetitive or rhythmic firing of Aps (cardiac,
thalamic)
Physiology of Voltage-Gated Ca2+ Channels
Image taken from Caterall 2011
Image taken from Caterall 2011
Image taken from Caterall 2011
Images taken from Caterall 2011
Images taken from Caterall 2011
Cav1 channel
• Excitation-contraction coupling
• Excitation-transcription coupling
• Excitation-secretion coupling
Excitation-contraction coupling
http://www.studyblue.com/notes/note/n/chapter-14-cardiovascular-
http://pharmaceuticalintelligence.com/2013/09/08/the-centrality-of-ca2-signaling-andcytoskeleton-involving-calmodulin-kinases-and-ryanodine-receptors-in-cardiac-failure-arterialsmooth-muscle-post-ischemic-arrhythmia-similarities-and-differen/
Regulation of excitation-contraction coupling
• PKA phosphorylation and its anchoring via a
kinase anchoring protein (APAK).
• An autoinhibited Ca2+ channel complex with
noncovalently bound distal carboxylterminus.
• Ca2+/ calmodulin-dependent inactivation
Image taken from Caterall 2011
Excitation-transcription coupling
• Calmodulin binds to the proximal caboxyterminal domain, the Ca2+ /calmodulin
complex moves to the nucleus
• The distal carboxy-terminal domain is
regulated by Ca2+ in neurons.
Image taken from Caterall 2011
Excitation-secretion coupling
• Initialization of the secretion of hormones from
endocrine cells and release of neurotransmitters.
• The distal carboxy-terminal domain plays an
autoregulatory role in some Cav 1 channel, such as
Cav1.3, Cav1.4.
Cav2 Channels
http://physrev.physiology.org/content/90/4/1461
Image taken from Caterall 2011
Cav2 specific information
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Initiate fast release of glutamate, GABA, and
acetylcholine
SNARE proteins
G Protein subunits are responsible for modulation
Additional binding proteins
Cav3 Channels
• Molecular structure:
• Negative potential activation (fast inactivation)
• Similar to Cav1 and 2 by 25%
• Functional
• Present in rhythmic structures:
• SA node (pacemaker), relay neurons of thalamus (sleep), adrenal cortex (aldosterone)
• Mutations can cause absence epilepsy (sleep-like state)
• Regulation
• Dopamine & NTMs
• Angiotensin II
Conlcusion
• Ca2+ channel complexes – effector and regulator
• Four cases effectors enhance Cav1 & Cav2
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Skeletal muscle
SNARE proteins
Ca2+/CaM-dependent protein kinase II
RIM
• Common Theme: “Effector Checkpoint”
Point of interest
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LOF for Nav1.7 causes anosmia
Cav2.2 is involved with the first synapse of the
olfactory system
Cacna1b LOF mutation causes an absence of Cav2.2
channels
Effects of Lacking Cav2.2 on Olfactory Sensory
Neurons (OSN) in the Main Olfactory Bulb (MOB)
and on Vomeronasal Sensory Neurons (VSN) in the
Accessory Olfactory Bulb (AOB)
Summary
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N-type Cav Channels are main contributors to
presynaptic release
MOB and AOB respond differently to Cav2.2
mutation
Presence of unknown Cav channel type in MOB
Lack of Cav2.2 does not cause anosmia
Mutation causes hyperaggressive behavior
Question?
• Ca2+ and Na+ own nearly identical diameters (2A)
• The extracellular concentration of Na+ is 70-fold higher than Ca2+
• The conductance of Na+ is more than 500-fold lower than Ca2+ via Cav channel
How the Cav channel keeps the high selectivity of Ca2+ ?
Selectivity filter
NavAb: 175TLESWSM181, outward sodium current
CavAb: 175TLDDWSD181 , inward calcium current
No significant alteration in backbone structure between NavAb and
CavAb------the selectivity is mainly determined by the side chains.
 Three Ca2+ - binding sites:
• Site 1: the carboxyl groups of D178.
• Site 2: four carboxylate oxygen atoms
from D177 and four backbone
carbonyl oxygen atoms from L176.
• Site 3: a plane of four carbonyls from
T175
 The bound Ca2+ ion is continuously
stabilized in a fully hydrated state through
the pore.
 D178 VS S178:
• Site 1
• Over 100-fold change in PCa:PNa.
• D178: forms the first hydrated Ca2+ binding site
• S178: blocks the conduction of Ca2+ by
directly binding Ca2+ and displacing
the hydration shell
 D177 VS E177:
• Site 2
• 5.5-fold change in PCa:PNa.
• D177: interacts with Ca2+
• E177: swings away from the
selectivity filter
 D181 VS N181 VS M181:
• Site 1
• 4- to 5-fold change in PCa:PNa.
• D181 an N181: constrains the side-chain of the D178 ring by forming a hydrogen bond.
• M181: unconstrains the side-chain of the D178 and results in a blocking Ca2+ tightly bound at Site1.
 Binding forces:
Site 2> Site 1 > Site 3
 Ca2+ can’t occupy adjacent sites
simultaneously due to electrostatic
repulsive interactions.
 High extracellular concentration of
Ca2+ and weak binding of Ca2+ to Site 3
generate a unidirectional flux of Ca2+ .
Direct Recording and molecular
identity of the calcium channel
of primary cilia
Daniel Blackman, Zhihui Zhou, Thomas Arnold
Primary Cilia
• Specialized
compartments
• Calcium signaling
• Hedgehog pathways
• Human retina
pigmented
epithelium cells
tagged with GFP
Image taken from DeCaen et al
Image taken from DeCaen et al
Image taken from DeCaen et al
Polycystin proteins (PC/PKD)
• Identified in polycystic kidney disease
• Form ion channels at high densities in multiple cell types
• Two structural classes (PKD1s and PKD2s)
• Hypothesis: PKD1L1-PKD2L1 heteromultermerize to form calciumpermeant ciliary channels
Image taken from DeCaen et al
Conclusion
• No Ca2+ current with just PKD1L1 (current observed with PKD2L1)
• Only with both PKD1L1 and PKD2L1 was current observed matching
human