Mathematical MReceptorReceptor

Gat

Anmar

PostdoctoLaboratory of Bi

National InstiNational Insti

Monday, M

Modeling of P2X7 r/Channelr/Channelting

r Khadra

oral Fellowiological Modeling itutes of Healthitutes of Health

May 23, 2011

1. An Overview

P2X7Rs are ATP-gated nonseon various cellson various cells.

Activation of these receptors cagrowth and differentiation.growth and differentiation.

lective cation channels expressed

an either cause cell death or cell

1. An Overview

There are 3 ATP-bindinggNegative cooperativity inReceptor sensitization (ATP b dATPs are bound.

g sites on P2X7Rs.gn ATP binding is observed.pore dilation) occurs when 3

1. Gating Propertie

P2X7Rs activate/deactivate eithalmost constant amplitude, or bcurrent amplitude and slowed de

es of P2X7R

her monophasically (I1), with iphasically (I1+ I2), with increased 1 2eactivation.

1. Gating Propertie

I1 rise was best fitted with a monoexponential pfunction. The rate of I1 growth increased with elevation in agonistelevation in agonist.

4-parameter logistic function was the best fitfunction was the best fit for I2 growth.

B i i fBest approximation for current deactivation was achieved using gmonoexponential or biexponential fittings.

es of P2X7R

1. Gating Propertie

Repetitive agonistRepetitive agonist stimulation led to receptor sensitization

d dil tiand pore dilation.

During repetitive stimulation, current amplitude increased pand the deactivation component slowed downdown.

es of P2X7R

2. Ca2+-Dependenc

Free-intracellular Ca2+ allosteric

ce

cally inhibited receptor activation.

2. Ca2+-Dependenc

Free-intracellular Ca2+ also facilated receptor pdeactivation.

ce

3. Modeling of P2X

Markov state model describingunbinding and sensitization/losP2X7Rs in a cell was used.

X7R Gating

g the sequence of binding and ss-of-sensitization events of

3. Modeling of P2X

F β2/(β2F=αβ2/(β2

X7R Gating

2 [DC] 2)2+[DC]e2)

3. Modeling of P2X

Monophasic and biphasic rMonophasic and biphasic r

X7R Gating

responses were generated.responses were generated.

3. Modeling of P2X

Receptor sensitization was also obtained during repetitive stimulation.

X7R Gating

4. Understanding

Ca2+ inhibits BzATP bCa2 inhibits BzATP-b

Ca2+ effects

binding to the receptorbinding to the receptor.

4. Understanding

Ca2+ facilitates receptor deactivation due to increased backward rates.

Ca2+ effects

5. Conclusions The two current phases may bcontradictory outcomes (apopt

Receptor sensitization (dilation)phase of the current. Supportedphase of the current. Supported

Negative cooperativity in ATP biti tisensitization.

Ca2+ acts as an allosteric inhibitCa acts as an allosteric inhibitforward rates and increasing th

e responsible for the seemingly osis vs cell differentiation).

) is responsible for the second d by the model.d by the model.

binding is lost during receptor

tor to P2X7R by slowing down thetor to P2X7R by slowing down the e backward rates.

5. Conclusions The two current phases may bcontradictory outcomes (apopt

Receptor sensitization (dilation)phase of the current. Supportedphase of the current. Supported

Negative cooperativity in ATP biti tisensitization.

Ca2+ acts as an allosteric inhibitCa acts as an allosteric inhibitforward rates and increasing th

e responsible for the seemingly osis vs cell differentiation).

) is responsible for the second d by the model.d by the model.

binding is lost during receptor

tor to P2X7R by slowing down thetor to P2X7R by slowing down the e backward rates.

5. Conclusions The two current phases may bcontradictory outcomes (apopt

Receptor sensitization (dilation)phase of the current. Supportedphase of the current. Supported

Negative cooperativity in ATP biti tisensitization.

Ca2+ acts as an allosteric inhibitCa acts as an allosteric inhibitforward rates and increasing th

e responsible for the seemingly osis vs cell differentiation).

) is responsible for the second d by the model.d by the model.

binding is lost during receptor

tor to P2X7R by slowing down thetor to P2X7R by slowing down the e backward rates.

5. Conclusions The two current phases may bcontradictory outcomes (apopt

Receptor sensitization (dilation)phase of the current. Supportedphase of the current. Supported

Negative cooperativity in ATP biti tisensitization.

Ca2+ acts as an allosteric inhibitCa acts as an allosteric inhibitforward rates and increasing th

e responsible for the seemingly osis vs cell differentiation).

) is responsible for the second d by the model.d by the model.

binding is lost during receptor

tor to P2X7R by slowing down thetor to P2X7R by slowing down the e backward rates.

6. Current/Future W

Use MCMC method to generategto describe the gating propertie

Extend this approach to other pExtend this approach to other pP2X2a and P2X2b receptors.

Estimate the number of binding

Work

e the best fit and the best scheme s of P2X7R.

purinergic receptors including thepurinergic receptors including the

g sites for Ca2+.

AcknowledgemenC ll b tCollaborators:-Arthur Sherman (Laboratory of B

- Zonghe Yan (Endocrinology andNICHD, NIH)

-Stanko Stojilkovic (EndocrinologBranch, NICH

Funding:

nts

Biological Modeling, NIDDK, NIH)

d Reproduction Research Branch,

gy and Reproduction ResearchHD, NIH)

ITBITB