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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
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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
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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
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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.
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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
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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
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2. Ca2+-Dependenc
Free-intracellular Ca2+ allosteric
ce
cally inhibited receptor activation.
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2. Ca2+-Dependenc
Free-intracellular Ca2+ also facilated receptor pdeactivation.
ce
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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
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3. Modeling of P2X
F β2/(β2F=αβ2/(β2
X7R Gating
2 [DC] 2)2+[DC]e2)
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3. Modeling of P2X
Monophasic and biphasic rMonophasic and biphasic r
X7R Gating
responses were generated.responses were generated.
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3. Modeling of P2X
Receptor sensitization was also obtained during repetitive stimulation.
X7R Gating
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4. Understanding
Ca2+ inhibits BzATP bCa2 inhibits BzATP-b
Ca2+ effects
binding to the receptorbinding to the receptor.
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4. Understanding
Ca2+ facilitates receptor deactivation due to increased backward rates.
Ca2+ effects
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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.
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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.
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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.
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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+.
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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