Transcript Dynamic Clamp

What is the dynamic clamp?
Accurate dynamic-clamp performance requires
uninterrupted, rapid sampling of the membrane
potential and fast computation of the current to
be injected.
Applications of the dynamic clamp
• Simulating voltageindependent conductances
• Adding or subtracting
voltaged-gated
conductances
Applications of the dynamic clamp
• Simulating synapses
• Coupling to model neurons
Applications of the dynamic clamp
• Simulating in vivo
conditions
Dynamic Clamp: Alteration
of Response Properties and
Creation of Virtual Realities
in Neurophysiology
Michael N. Economo, Fernando R.
Fernandez, and John A. White
Applications of Dynamic Clamp
• Applying a certain type of current.
• Modeling a synapse.
• Modeling a whole cell.
• Role of cells in a network.
• Feedback mechanisms.
• Creating in vivo like conditions.
• Hybrid systems.
Importance of stochasticity of INaP in sub-threshold oscillations stellate
cells. (Dorval and White 2005)
Sub-threshold oscillations of INaP
is the source of membrane
potential noise.
This is resulted from relatively
small number of NaP channels
with high single channel
conductance.
They block INaP and inject current
with dynamic clamp.
They inject current in a
stoschastic and deterministic
way and compare difference.
Producing in vivo like conditions (Destexhe et al., 2003)
Neurons in the nervous
system receives a lot of
synaptic input.
This inputs reduces input
resistance and time
constants by 80% nad
provide a huge
depolarization.
Dynamic clamp is used to
provide in vivo like
conditions in vitro by
applying high rates of
artificial inputs.
Hybrid Networks
A real cell can be connected to
one or more in silico artificial
cells.
Synchronization between
reciprocally connected cells in a
network can be studied.
Could be used for model
validation. Model can be tested
in vitro with a real cell.
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Spike time differences between a stellate cell and an artificial cell simulated.
Different virtual connections used as shown in figure.
Different patterns of synchronized activity recorded.
(Netoff et al., 2005)
Feedback control
• Dynamic clamp is used to
knock-in conductances which
have no physiological
correlate.
• After-hyperpolarization (AHP)
reducing and enhancing
currents injected.
• It is shown that spike train
rhythmicity is determined by
the shape of AHP.
• These currents manipulate
the voltage trajectory
following a spike.
Entorhinal stellate cells (Fernandez and White 2008)
Dynamic-clamp: Limitations
- Hardware / software capacity and price
- Conversion between analog and digital signals
- Time error/ frequency rate
- Conductances simulated are restricted to the site of injection
- Duplicates the electrical but not the signal conductances consequences
- Voltage measurement errors (single/double pipette; access resistance)
- Model error
- Traditional errors
Introduction
- Substantia Nigra (SN) dopamine (DA) neurons exhibit slow intrinsic pacemaker activity
- Voltage-gated sodium channels (Nav) contribute to the slow depolarization (DP) phase leading to action
potential (AP) initiation in the axon initial segment (AIS) and propagation.
- DP block is preceded by attenuation of AP, amplitude, broadening of each successive spike, and the eventual
failure of AP production
What is the role of NaV channels in SN DA neuron activity?
Sodium channels and SN DA neuron model description
http://neuromorpho.org/neuroMorpho/rotatingImages/DAN-04-R.CNG.gif
Inward currents of the AIS and soma are reduced during DP block induction
dV/dt = I/Cm
Inward currents of the AIS and soma are reduced during DP block induction
250 pA injection – n = 9
30 nS gNMDA injection – n = 7
Reduction of AIS and somatic Nav current increases susceptibility to DP block
Addition of somatic Nav current decreases susceptibility to DP block
Addition of virtual anti-Nav channels to the soma hastens to DP block
Replacing native Nav with virtual Nav reconstitutes pacing at a higher frequency
Simulation predictions of frequency with differential somatodendritic Na v
channel distribution
• Rat somatotrophs and lactotrophs -> bursting
• Gonadotrophs -> spiking
• Difference due BK current
MODEL
Membrane potential
Model
Predictions
Random gK,
gSK, gCa
Pharmacology blockage and
Dynamic Clamp
-gBK
Higher density of fast-activating gBK
-> higher burstiness
Activation
time
constant
Spiking
gonadotrophs
to bursters
Conclusions
• gBK
• Time constant for BK
Sources
• http://www.hormone.org/questions-and-answers/2010/hyperprolactinemia
Transient outward K+ current reduction
prolongs APs and promotes after
depolarizations: a dynamic clamp study in
human and rabbit cardiac atrial myocytes.
A. J. Workman, G. E. Marshall, A. C. Rankin, G. L. Smith and J.
Dempster
Key Points
• The effects of a transient outward K+ current (ITO) on AP shape and
duration in atrial myocytes are investigated.
• Dynamic clamp is used for blocking this current, since ITO blocking
drugs are non-selective. (For example; 4-AP blocks IKur with a more
than 40 times greater affinity than ITO)
Computational Model
Modeling ITO
Activation, Inactivation and Time Constants
Rabbit Myocytes: AP Response to ITO Subtraction
APD
Human Myocytes: AP Response to ITO Subtraction
APD
Effect of ITO on Different Phases (Human)
(ITO Subtraction Interrupted at indicated time points)
CADs : Cellular Arrhythmic Depolarization
Evidence for Delayed After Depolarization (DAD) (Rabbit)
Modulating CADs with ISO and ITO Subtraction
Within Train CADs
Production of Early After Depolarizations (EADs) by ITO
Subtraction and β-Stimulation
Suppression of CADs by interrupting ITO Subtraction,
Adding ITO and β1-Antogonist
CONCLUSION
• Dynamic clamp can be used to better
understand the roles of specific currents.
• Dynamic Clamp is used to neutralize a
transient outward current by injecting current
at opposite direction.
• They showed the importance of a transient
outward K+ current on normal heart
functioning.