HERG K+ channels spike-frequency adaptation (Chiesa et al 1997)

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Spike frequency adaptation has contributions from the IHERG current (encoded by the human eag-related gene (HERG); Warmke & Ganetzky, 1994), which develops with slow kinetics during depolarization and contributes to the repolarization of the long action potentials typically present in the heart. IHERG is one of the delayed rectifier currents (IK(r)) of the heart, and HERG mutations are associated with one of the cardiac arrhythmia LQT syndromes (LQT2). See paper for more and details.
1 . Chiesa N, Rosati B, Arcangeli A, Olivotto M, Wanke E (1997) A novel role for HERG K+ channels: spike-frequency adaptation. J Physiol 501 ( Pt 2):313-8 [PubMed]
Model Information (Click on a link to find other models with that property)
Model Type: Neuron or other electrically excitable cell;
Brain Region(s)/Organism:
Cell Type(s): Neuroblastoma;
Channel(s): I_HERG;
Gap Junctions:
Simulation Environment: XPP;
Model Concept(s): Action Potentials; Long-QT; Spike Frequency Adaptation;
Implementer(s): Wu, Sheng-Nan [snwu at mail.ncku.edu.tw]; Chang, Han-Dong; Wu, Jiun-Shian [coolneon at gmail.com];
Search NeuronDB for information about:  I_HERG;
% Spike adaptation by erg-like K+ current.  If girbar is altered (0.5->0), 
% spike discharge will be changed.  
% Written by Dr. Sheng-Nan Wu, Dept Physiol, Natl Cheng Kung U Med Coll.
% Ref: Chiesa et al., J Physiol 1997;501:313-318

% Initial values of the variables
init v=-72.0, nK=0.288, hK=0.367, mNa=0.041,  hNa=0.844, nIR=0.003, rIR=0.282

% Values of the model parameters
params iapp=1.2, cm=1, gnabar=15, gkbar=2.5, girbar=0.5, gl=0.05, vna=50, vk=-80, vir=-80, vl=-80

% Gating functions
alphaNam(v) = 0.1*(v+40)/( 1 - exp(-0.09*(v+40)))
betaNam(v) =  4*exp(-0.055*(v+70))
mNainf(v) = 1/(1+betaNam(v)/alphaNam(v))
tauNam(v) = 1/(alphaNam(v) + betaNam(v))

alphaNah(v) =  0.07*exp(-0.05*(v+70))
betaNah(v) = 1/( 1 + exp(-0.09*(v+25)) )
hNainf(v) = 1/(1+betaNah(v)/alphaNah(v))
tauNah(v) = 1/(alphaNah(v) + betaNah(v))

alphaKn(v) = 0.01*(v + 60)/(1 - exp(-0.1*(V + 60)))
betaKn(v) = 0.125*exp(-0.0125*(V + 70))
nKinf(v) = 1/(1+betaKn(v)/alphaKn(v))
tauKn(v) = 1/(alphaKn(v) + betaKn(v))

alphaKh(v) = 0.001*exp(-0.04*(v+70))
betaKh(v) = 0.001*exp(-0.0195*(v+40))
hKinf(v) = 1/(1+betaKh(v)/alphaKh(v))
tauKh(v) = 1/(alphaKh(v) + betaKh(v))

alphaIRn(v) = 0.09/(1+exp(0.11*(v+100)))
betaIRn(v) = 0.00035*exp(0.07*(v+25))
nIRinf(v) = 1/(1+betaIRn(v)/alphaIRn(v))
tauIRn(v) = 1/(alphaIRn(v) + betaIRn(v))

alphaIRr(v) = 30/(1+exp(0.04*(v+230)))
betaIRr(v) = 0.15/(1+exp(-0.05*(v+120)))
rIRinf(v) = 1/(1+betaIRr(v)/alphaIRr(v))
tauIRr(v) = 1/(alphaIRr(v) + betaIRr(v))

% Apply current injection
par tpulse=610
par tfirst=10
istim = iapp*(heav(t-tfirst)-heav(t-tpulse))

% The differential equations
v' =  -(gnabar*mNa^3*hNa*(v-vna) + gkbar*nK^4*hK*(v-vk) + girbar*nIR*rIR*(v-vir) + gl*(v-vl) - istim)/cm
mNa' =  (mNainf(v) - mNa)/tauNam(v)
hNa' =  (hNainf(v) - hNa)/tauNah(v)
nK' =  (nKinf(v) - nK)/tauKn(v)
hK' = (hKinf(v) - hK)/tauKh(v)
nIR' = (nIRinf(v) - nIR)/tauIRn(v)
rIR' = (rIRinf(v) - rIR)/tauIRr(v)

% Numerical and plotting parameters for xpp
@xlo=0, xhi=700, ylo=-90, yhi=+60, total=700, dt=0.05, method=Euler, LT=1

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