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

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: 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

Cell Structure

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

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.

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

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

Ca2+ spreading wave Ian Parker, UC Irvine

Lechleiter, Girard, Peralta and Clapham, Science, 1991 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 Ca2+ waves at higher [IP3] Local Ca2+ puffs at low [IP3] Marchant & Parker, EMBO J. 1999

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

Multi-scale Ca2+ Signals

Single IP3R Channel Model

- 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

Tetrameric Structure of IP3R Hamada, et al, JBC 2003

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

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

Ca2+ Blips with Single IP3R Channel

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

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

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

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

Slower Decay of [Ca2+] due to Immobile Buffer

Faster Decay of [Ca2+] with Mobile Buffer

Ca2+ Puffs with Clustered IP3R channels

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

A Cluster of 9 IP3Rs

Effects of Immobile Buffers

Effects of Fast Mobile Buffer [BAPTA] mM

[Ca2+] in the Cluster Time (ms)

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

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).

Ca2+ Waves at Global Cell Level

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

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

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

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 !!!

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

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

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

Noise-induced Ca2+ waves

From Stochasticity To Periodicity at biologically realistic cluster distribution Channel number per Cluster 1 4 9 16 25 36 64 100 Characteristic time of self-correlation T Shuai and Jung, PNAS 2003

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

Puff-induced Ca2+ waves

Bifurcation of calcium signal

+ Interaction of channel noise and IP3 noise Channel noise only

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

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.

Summary

Thanks University of California, Irvine Prof. Ian Parker Los Alamos National Lab John E. Pearson Ohio University Prof. Peter Jung NSF China (2008-2010) NIH USA (2009-2012) University of Pennsylvania Prof. J. Kevin Foskett Dr. Don-On Daniel Mak Humboldt-Univeristy at Berlin Dr. Sten Ruediger