NEURON Note #25


Goals: Create a NMODL model for the delayed rectifier potassium current (KDR)


Introduction:

Delayed rectifier potassium current (IDR, KDR, or IK) is an important outward current regulating the firing properties of excitable cells. Thus, it is wise to carefully select an available model or create one based on experimental data. I tested the models in Bianchi et al's paper (2012), Gonzalez et al's paper (2011), and Migliore's paper (1996). These models generate currents which are distinct from IDR observed in CA1 pyramidal neurons. Thus, I created a new model based on Mohapatra et al's data (2009) and Hoffman's data (1997). This model is more suitable to simulate IDR in CA1 pyramidal neurons.


Results:

Bianchi (2012)

Voltage and Current GV Curve Time Constant
 Vhalf = 13.0 (mV); k = -8.8 (mV) 

Gonzalez (2011)

V1/2 is too hyperpolarized. The absolute value of k is too small.

Voltage and Current Traces GV Curve Tau
 Vhalf = -31.9 (mV); k = -4.1 (mV) 

Migliore (1996)

V1/2 is too hyperpolarized.

Voltage and Current Traces GV Curve Time Constant
 Vhalf = -41.7 (mV); k = -1.4 (mV) 

Payne's Model

g = gbar * n^4 * l

Target Activation Curve:
Vhalf = 2 (mV) (Ref: Chen (2004)
k = 7 (mV) (Ref: Chen (2004)

n (activation particle):
Vhalf = -13.9 (mV)
k = -9.1 (mV)
tau = 1.8 (ms) (Ref: Hoffman (1997))

l (inactivation particle):
Vhalf = -28.8 (mV) (Ref: Mohapatra (2009)
k = 11.4 (mV) (Ref: Mohapatra (2009)
tau = 500 (ms) (Ref: Mohapatra (2009)
P = 0.25 (1) (Ref: Mohapatra (2009)

Program used to find parameters for n: BoltzmannPowerFit.py
Command to run the program in the cmd console: ipython3 BoltzmannPowerFit.py -- pylab

Control Panel Curves

NMODL file: kdr_p.mod

Results

Voltage and Current Traces Normalized Conductance Inactivation Tau
Activation Tau
 Vhalf = 1.9 (mV); k = -6.9 (mV) 

References: