1. The Dynamics of Intracellular Ca2+ Signals
Jianwei Shuai, Ohio University
The Dynamics of Intracellular Ca2+ Signals
Jianwei Shuai (帅建伟)
Department of Physics
Xiamen University
GRC Nonlinear Science in Mt. Holyoke College

2. 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

3. Fixed Ca2+ via Moving Ca2+

4. Moving Calcium Ions In-between: Life beginning Life ending
A life and death signal in cells
Life beginning
Sperm
Ca2+
Oscillation
Cell
Division
Egg
Life ending
High
Calcium
Concentration
protein-digesting
enzymes
Cell
Death
In-between:
Brain memory
Ca2+-related diseases: Cancer, Alzheimer’s
Communication between cells,
Communication among different organelles within a cell

5. Cell Structure

6. Ca2+ Release Dynamics Cytosol ER IP3R IP3 Membrane [Ca]Local>10mM
Pump
IP3R ER
Cell
Membrane
Pump

7. Ca2+-induced Ca2+ release propagates Ca2+ waves
Cytosol
Membrane ER
Low [Ca] opens the IP3R channels: fast binding;
High [Ca] inhibits the IP3R channels: slow binding.

8. How does Ca2+ act as a cellular signal?
Ca2+ concepts
Ca2+ Concentration
Ca2+ Oscillation
Spatiotemporal
Ca2+ wave
Cellular information is encoded by the spatiotemporal Ca2+ patterns
(e.g. frequency and amplitude of oscillation).
Ca2+ Signal

9. Technique to Visualize Cytosolic Ca2+
Calcium
Fluorescence
dye
Green light
Blue light
Blue light
Blue light

10. Ca2+ spreading wave
Ian Parker, UC Irvine

11. Lechleiter, Girard, Peralta and Clapham, Science, 1991
Ca2+ spiral wave
Lechleiter, Girard, Peralta and Clapham, Science, 1991

12. Fine structure underlying Ca2+ waves
Marchant & Parker, EMBO J. 1999

13. Ca2+ waves consist of puffs
Ca2+ waves at higher [IP3]
Local Ca2+ puffs at low [IP3]
Marchant & Parker, EMBO J. 1999

14. Jianwei Shuai, Ohio University
Puff is triggered by blip
Blip
Puff
Temporal Profile
Heather, Dargan, Shuai and Parker, Biophys J. 2006
GRC Nonlinear Science in Mt. Holyoke College

15. Multi-scale Ca2+ Signals

16. Single IP3R Channel Model

17. - The IP3R channel model + +
Three independent and equivalent subunits.
Each subunit
IP3 + Ca -
has 8 states:
110
IP3 + Ca
The open subunit is
Channel is open
when 3 subunits are open
DeYoung & Keizer, PNAS 1992

18. Tetrameric Structure of IP3R
Hamada, et al, JBC 2003

19. IP3R model with 4 Subunits
Each channel has four independent and equivalent subunits.
IP3
Open Channel
3 active
subunits
4 active
subunits

20. The IP3R model with conformational change
Shuai, et al, Biophys J. 2007

21. Ca2+ Blips with Single IP3R Channel

22. Model Design
6mm
Mobile Buffer
6mm
Immobile Buffer
Free Ca2+
6mm

23. Markovian simulation of channel dynamics
Stochastic binding/unbinding dynamics:
IP3
100
Random
Number ?
110
a5[Ca]dt
a2[Ca]dt 1
b1dt
b1dt
a2[Ca]dt
a5[Ca]dt
IP3 - Ca
101
IP3 + Ca
110
000
Shuai & Jung, Biophys J 2002

24. [Ca2+] distribution around the channel mouth
400mM
[Ca2+] mM
20mM
[Ca2+]~400mM
[Ca2+]~20mM
15nm
Cytosol ER

25. Effects of Ca2+ Buffers
Shuai, et al,
Biophys J.
2008

26. Slower Decay of [Ca2+] due to Immobile Buffer

27. Faster Decay of [Ca2+] with Mobile Buffer

28. Ca2+ Puffs with Clustered IP3R channels

29. Puff Model L L : Cluster width N : Total number of open
6mm
6mm L
Immobile Buffer
L : Cluster width
N : Total number of open
channels during a puff
Free Ca2+
EGTA
Fluo4 Dextran
6mm

30. A Cluster of 9 IP3Rs

31. Effects of Immobile Buffers

32. Effects of Fast Mobile Buffer
[BAPTA] mM

33. [Ca2+] in the Cluster
Time (ms)

34. Modified [Ca2+] by BAPTA
[BAPTA] mM
Ruediger, Shuai, et al, Submitted

35. Conclusion 1
Ca2+ 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).

36. Ca2+ Waves at Global Cell Level

37. Ca2+ wave model Cytosol ER Channel cluster Free Ca2+ Stationary Buffer
Mobile Buffer
Channel cluster ER

38. A stochastic Ca2+ model with clustered channelsy x
Cluster distance 3 mm
Each cluster 36 channels

39. With low [IP3] stimulus ?
[Ca2+]
[IP3]

40. What will happen if we change cluster distributions?
Cell size:
Cluster distance 0.5 mm
Each cluster 1 channel
Cluster distance 3 mm
Each cluster 36 channels
Cluster distance 5 mm
Each cluster 100 channels
Total channels: 14,400
Fixed !!!

41. No wave with low [IP3] at small cluster distance
Cluster distance 0.5 mm
Each cluster 1 channel

42. No wave with low [IP3] at large cluster distance
Cluster distance 5 mm
Each cluster 100 channels

43. At middle cluster distance Ca2+ waves generated with low [IP3]
Cluster distance 3 mm
Each cluster 36 channels

44. Noise-induced Ca2+ waves

45. From Stochasticity To Periodicity at biologically realistic cluster distribution
Channel number per Cluster
Characteristic time
of self-correlation T
Shuai and Jung, PNAS 2003

46. With high [IP3] stimulus?
[Ca2+]
[IP3]

47. Puff-induced Ca2+ waves

48. Bifurcation of calcium signal

49. + Interaction of channel noise and IP3 noise Channel noise only

50. Restoration of Periodicity by Noise Suppressing Noise
Liao, Jung, Shuai, PRE (2009)

51. The novel roles of molecular noise in Ca2+ system
Conclusion 2
The 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.

52. Summary

53. Thanks University of California, Irvine Prof. Ian Parker
Los Alamos National Lab
John E. Pearson
Ohio University
Prof. Peter Jung
NSF China ( )
NIH USA ( )
University of Pennsylvania
Prof. J. Kevin Foskett
Dr. Don-On Daniel Mak
Humboldt-Univeristy at Berlin
Dr. Sten Ruediger