The Dynamics of Intracellular Ca2+
Signals
Jianwei Shuai (帅建伟 )
Department of PhysicsXiamen University
Outline
• Introduction
• IP3R Ca2+ channel model
• Ca2+ blips with single IP3R Ca2+ channel
• Ca2+ puffs with clustered Ca2+ channels
• Ca2+ waves at the global cell level
• Summary
Fixed Ca2+ via Moving Ca2+
Moving Calcium Ions
In-between:• Brain memory• Ca2+-related diseases: Cancer, Alzheimer’s • Communication between cells,• Communication among different organelles within a cell
Life beginning
Life ending
A life and death signal in cells
SpermCa2+
OscillationCell
DivisionEgg
CellDeath
HighCalcium
Concentration
protein-digesting enzymes
Cell Structure
Ca2+ Release Dynamics
Cell Membrane
Pump ER
IP3 Cytosol
IP3RPump
M 1.0]Ca[ Rest
[Ca]Local>10M
ChannelJ
ER
CytosolCaD
Membrane
Ca2+-induced Ca2+ release propagates Ca2+ waves
Low [Ca] opens the IP3R channels: fast binding;
High [Ca] inhibits the IP3R channels: slow binding.
How does Ca2+ act as a cellular signal?
Cellular information is encoded by the spatiotemporal Ca2+ patterns
(e.g. frequency and amplitude of oscillation).
Ca2+ Concentration
Ca2+ Oscillation
SpatiotemporalCa2+ wave
Ca2+ Signal
Ca2+ concepts
Technique to Visualize Cytosolic Ca2+
Green light
Blue light Blue light
Blue light
CalciumFluorescence
dye
Ca2+ spreading wave
Ian Parker, UC Irvine
Ca2+ spiral wave
Lechleiter, Girard, Peralta and Clapham, Science, 1991
Fine structure underlying Ca2+ waves
Marchant & Parker, EMBO J. 1999
Ca2+ waves consist of puffs
puff
Ca2+ waves at higher [IP3] Local Ca2+ puffs at low [IP3]
Marchant & Parker, EMBO J. 1999
Puff is triggered by blip
Temporal Profile
Heather, Dargan, Shuai and Parker, Biophys J. 2006
Blip
Puff
Multi-scale Ca2+ Signals
Single IP3R Channel Model
The IP3R channel model
Three independent and equivalent subunits.
DeYoung & Keizer, PNAS 1992
The open subunit is
101
111
100
010
000
011
001
Activa
tion C
a2+
IP3
Inhibitory Ca2+
b61
b62
b52
b41
b32
b21
b11
b51
b42
b31
b22
b12
a61
c
a52
c
a51
c
a42
c
a41
c
a31
p
a32
p
a21
c
a12
p
a62
c
a22
c
a11
p
110
has 8 states: Each subunit IP3 +Ca
-Ca
IP3 +Ca
110122
2251
010312111221002
51110
)]Ca[(
]IP[]Ca[
xbab
xaxbxadt
dx
Channel is open when 3 subunits are open
3110
Total
Open )(xN
N
Tetrameric Structure of IP3R
Hamada, et al, JBC 2003
IP3R model with 4 Subunits
Open Channel
Each channel has four independent and equivalent subunits.
3 activesubunits
4 activesubunits
IP3
0.01 0.1 1 10 100 10000.0
0.2
0.4
0.6
0.8
1.0
Mak Experiment IP3 = 0.01 M (2003) IP3 = 0.02 M (2003) IP3 = 0.033 M (2003) IP3 = 0.033 M (1998) IP3 = 10.0 M (2003)
[IP3]=10.0 M
0.033
0.02
0.01
Op
en
pro
ba
bili
ty
Ca2+ (M)
The IP3R model with conformational change
Active01100Active Xbxadt
dX
1100Active0
110152
21002
5111201031110 )]Ca[(]Ca[]IP[
xaXb
xbbaxaxbxadt
dx
)1(4 Active3Active
4ActiveOpen XXXP
Shuai, et al, Biophys J. 2007
Ca2+ Blips
with Single IP3R Channel
Model Design
6m
6m
6m
Free Ca2+
Immobile Buffer
Mobile Buffer
])MobCa[[Mob](]Ca[]MobCa[
])ImmCa[[Imm](]Ca[]ImmCa[ )0,,( ]Ca[]Ca[
T2
MM
T2
SSCh22
Ca
2
JzyxDt
]MobCa[])MobCa[[Mob](]Ca[
]MobCa[]MobCa[
MT2
M
2MobCa
Dt ]ImmCa[])ImmCa[[Imm](]Ca[
]ImmCa[ST
2S
t
Markovian simulation of channel dynamics
Stochastic binding/unbinding dynamics:
101
111
100
010
000
011
001
IP3
Inhibitory Ca2+
a2[Ca]dta5[Ca]dt
b1dt
110
b1dta2[Ca]dt a5[Ca]dt
IP3
100
IP3 -Ca
101
IP3 +Ca
110 000
0 1
RandomNumber?
Shuai & Jung, Biophys J 2002
[Ca2+] distribution around the channel mouth
15nm
[Ca2+]~400M [Ca2+]~20M
ER
Cytosol
1
10
100
500
5 5 15 100015100
20M
400M
[Ca2
+] M
Effects of Ca2+ Buffers
0.1 1 10 100 1000 100000.0
0.2
0.4
0.6
PO
[Ca2+ Buffer] (M)
C0
3
6
9
O
(ms)
1
10
100
C (
ms)
A
B
BAPTA EGTA Immobile
Shuai, et al, Biophys J. 2008
Slower Decay of [Ca2+]due to Immobile Buffer
0.1
110
[Immobile] = 800 M
100
[Ca2
+] M
Time (ms)
[EGTA] = 0 M
100010000100
0 10 20 30 40 50
0.1
110
[Immobile] = 800 M
1
100
Time (ms)
[BAPTA] = 0 M
1001000
10
0 10 20 30 40 50
Faster Decay of [Ca2+]with Mobile Buffer
Ca2+ Puffs
with Clustered IP3R channels
Puff Model
6m
6m
6m
L : Cluster widthN : Total number of open channels during a puff
L
Free Ca2+
Immobile Buffer
EGTA
Fluo4 Dextran
])CaEG[[EG](]Ca[]CaEG[])FlCa[[Fl](]Ca[]FlCa[
])ImCa[[Im](]Ca[]ImCa[ )0,,( ]Ca[]Ca[
T2
EET2
FF
T2
ImImCh22
Ca
2
JzyxDt
]FluoCa[])FluoCa[[Fluo](]Ca[
]FluoCa[]FluoCa[
FT2
F
2FluoCa
Dt ]StatCa[])StatCa[[Stat](]FreeCa[
]StatCa[STS
t
A Cluster of 9 IP3Rs
Effects of Immobile Buffers
Effects of Fast Mobile Buffer
[BAPTA] M
[Ca2+] in the Cluster
Time (ms)
Modified [Ca2+] by BAPTA
[BAPTA] M
0.01 0.1 1 10 100 10000.0
0.2
0.4
0.6
0.8
1.0
Mak Experiment IP3 = 0.01 M (2003) IP3 = 0.02 M (2003) IP3 = 0.033 M (2003) IP3 = 0.033 M (1998) IP3 = 10.0 M (2003)
[IP3]=10.0 M
0.033
0.02
0.01
Ope
n pr
obab
ility
Ca2+ (M)
Ruediger, Shuai, et al, Submitted
Conclusion 1Ca2+ Buffers function differently at single and clustered channel levels.
• The open probability for a single IP3R:– increases with increasing immobile buffer– has little change with the mobile buffer
• The open probability for a clustered IP3Rs:– has little change with the immobile buffer– shows a biphasic mode with the increase of
fast mobile buffer (BAPTA).
Ca2+ Waves
at Global Cell Level
ClusterJ
ER
Cytosol
PumpJ
CaD
Ca2+ wave model
])MobC[[Mob](]Ca[]MobCa[
])StatCa[[Stat](]Ca[]StatCa[ )0,,( ]Ca[]Ca[
T2
MM
T2
SSCluster22
Ca
2
JzyxDt
]StatCa[])StatCa[[Stat](]FreeCa[]StatCa[
STS
t
]MobCa[])MobCa[[Mob](]Ca[]MobCa[]MobCa[
MT2
M2
MobCa
Dt
Free Ca2+Stationary Buffer
Mobile Buffer Channel cluster
m 60
y
x
A stochastic Ca2+ model with clustered channels
Cluster distance 3 mEach cluster 36 channels
With low [IP3] stimulus
?
[IP3]
[Ca2+]
Total channels: 14,400
m 60m 60 Cell size:
What will happen if we change cluster distributions?
Cluster distance 0.5 m Each cluster 1 channel
Cluster distance 3 m Each cluster 36 channels
Cluster distance 5 mEach cluster 100 channels
Fixed !!!
No wave with low [IP3]at small cluster distance
0 500 1000 1500 20000.0
0.1
0.2
0.3
Ca2+
(M)
Time (sec)
0.0
0.1
0.2
0.3
Averaged calcium
Calcium at center cluster
M25.0[IP3]
Cluster distance 0.5 m Each cluster 1 channel
No wave with low [IP3]at large cluster distance
0 500 1000 1500 20000.0
0.1
0.2
0.3
Ca2+
(M)
Time (sec)
0.0
0.1
0.2
0.3
Averaged calcium
Calcium at center cluster
M25.0[IP3]
Cluster distance 5 mEach cluster 100 channels
At middle cluster distance Ca2+ waves generated with low [IP3]
M25.0[IP3] 0 500 1000 1500 20000.0
0.1
0.2
0.3
Ca2+
(M)
Time (sec)
0.0
0.1
0.2
0.3
Averaged calcium
Calcium at center cluster
Cluster distance 3 m Each cluster 36 channels
Noise-induced Ca2+ waves
From Stochasticity To Periodicity at biologically realistic cluster distribution
Shuai and Jung, PNAS 2003
0
2 )( dtT
Characteristic time of self-correlation
211
2
11
1111
)()(
)()()(
xtxxtx
xtxxtx
Channel number per Cluster1 4 9 16 25 36 64 100
1 2 3 4 50
5
10
15
2.51.50.5
DCa
=20 m2/secIP
3=0.21 M
Cluster Distance (m)
T
With high [IP3] stimulus
?
[IP3]
[Ca2+]
Puff-induced Ca2+ waves
Bifurcation of calcium signal
Channel noise only
Channel noise only
Channel noise
+IP3 noise
Interaction of channel noise and IP3 noise
Liao, Jung, Shuai, PRE (2009)
Restoration of Periodicity by Noise Suppressing Noise
Conclusion 2The novel roles of molecular noise in Ca2+ system
• At resting state with low [IP3] concentration:– The channel noise with clustered IP3Rs can
generate the periodic Ca2+ waves
• At oscillatory state with high [IP3]:– The channel noise will destroy the periodic Ca2+
oscillation– The additional IP3 noise with certain strength
can partly restore the periodicity of Ca2+ signals.
Summary
University of California, Irvine Prof. Ian Parker
Ohio University Prof. Peter Jung
Thanks
Los Alamos National Lab John E. Pearson
University of Pennsylvania
Prof. J. Kevin Foskett
Dr. Don-On Daniel Mak
Humboldt-Univeristy at Berlin Dr. Sten Ruediger
NSF China (2008-2010)NIH USA (2009-2012)
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