NEURON Note #26

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

Introduction:

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

Notes about methods:

e_K = -85 (mV)

Results:

Summary

Bianchi (2012)

kap (Proximal K_A)

gka = gkabar * n * l

Calculated from the model

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

Activation

	Activation: V1/2 = 22.1 (mV); k = -17.6 (mV)

Inactivation

	Inactivation: V1/2 = -56.0 (mV); k = 8.8 (mV)

Royeck (2008)

g = gbar * n³ * l

Calculated from the model

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

	Activation: V1/2 = -21.9 (mV); k = -15.5 (mV)

Inactivation

	Inactivation: V1/2 = -79.9 (mV); k = 6.0 (mV)

Payne's K_A model

g = gbar * m⁴ * h

NMODL file: ka_p.mod

Calculate Vhalf and k

V1/2 = -31.3 (mV); k = -20.8 (mV)

Calculated from the model

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

	Activation: V1/2 = 6.3 (mV); k = -15.3 (mV)

Inactivation

	Inactivation: V1/2 = -64.0 (mV); k = 9.0 (mV)

References:

• Bianchi D, Marasco A, Limongiello A, Marchetti C, Marie H, Tirozzi B, Migliore M. On the mechanisms underlying the depolarization block in the spiking dynamics of CA1 pyramidal neurons. J Comput Neurosci. 2012 Feb 5.
• Royeck M, Horstmann MT, Remy S, Reitze M, Yaari Y, Beck H. Role of axonal NaV1.6 sodium channels in action potential initiation of CA1 pyramidal neurons. J Neurophysiol. 2008 Oct;100(4):2361-80.
• Hoffman DA, Magee JC, Colbert CM, Johnston D. K+ channel regulation of signal propagation in dendrites of hippocampal pyramidal neurons. Nature. 1997 Jun 26;387(6636):869-75.
• Chen X, Johnston D. Properties of single voltage-dependent K+ channels in dendrites of CA1 pyramidal neurones of rat hippocampus. J Physiol. 2004 Aug 15;559(Pt 1):187-203.