NEURON Note #26


Goals: Create a model for the fast, transient A-type potassium current (IA)


Introduction:

A-type potassium current (IA) is important for signal processing and excitability tuning in dendrites. Thus, it is critical to have a good IA model to simulate signals in dendrites. I examined two IA models and found they did not match published results very well. Therefore, I created an IA model based on the data in two articles, Hoffman et al (1997) and Chen et al (2004).


Notes about methods:

eK = -85 (mV)


Results:

Summary

Bianchi Royeck Payne Hoffman Chen
Activation Vhalf (mV) 22.1 -21.9 6.3 11 5
Activation k (mV) -17.6 -15.5 -15.3 -18 -16
Inactivation Vhalf (mV) -56.0 -79.9 -64.0 -56 -64
Inactivation k (mV) 8.8 6.0 9.0 8 9

Activation and Inactivation
Activation Tau Inactivation Tau


Bianchi (2012)

kap (Proximal KA)

gka = gkabar * n * l

Calculated from the model

Gating Particle State Tau
n (activation): V1/2 = 11.2 (mV); k = -17.1 (mV)
l (inactivation): V1/2 = -56.0 (mV); k = 8.8 (mV)
 

Activation

Voltage and Current Traces GV Curve
Activation Tau
Tau
  Activation: V1/2 = 22.1 (mV); k = -17.6 (mV)  

Inactivation

Voltage and Current Traces
Inactivation GV Curve
  Inactivation: V1/2 = -56.0 (mV); k = 8.8 (mV)

Royeck (2008)

g = gbar * n3 * l

Calculated from the model

State Tau
n (activation): V1/2 = -50.0 (mV); k = -20 (mV)
l (inactivation): V1/2 = -80.0 (mV); k = 6.0 (mV)
Activation: 0.5 (ms)
Inactivation: 15 (ms)

Activation

Voltage and Current GV Curve Tau
  Activation: V1/2 = -21.9 (mV); k = -15.5 (mV)  

Inactivation

Voltage and Current Traces GV Curve
  Inactivation: V1/2 = -79.9 (mV); k = 6.0 (mV)

Payne's KA model

g = gbar * m4 * h

NMODL file: ka_p.mod

Calculate Vhalf and k

 Control Panel  Curve Fitting
V1/2 = -31.3 (mV); k = -20.8 (mV)  

Calculated from the model

 States  Tau
m (activation): V1/2 = -31.3 (mV); k = -20.8 (mV)
h (inactivation): V1/2 = -64.0 (mV); k = 9 (mV)
Activation: 0.2 (ms)

Activation

 Voltage and Current Traces  GV Curve  Tau
Activation Tau
  Activation: V1/2 = 6.3 (mV); k = -15.3 (mV)  

Inactivation

 Voltage and Current Traces  Inactivation Curve
  Inactivation: V1/2 = -64.0 (mV); k = 9.0 (mV)

References: