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README.md

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+# Clancy CE, Rudy Y. Cellular consequences of HERG mutations in the long QT syndrome: precursors to sudden cardiac death. Cardiovasc Res 2001;50:301-313.
+
+## Abstract:
+
+**BACKGROUND:** A variety of mutations in HERG, the major subunit of the rapidly activating component of the cardiac delayed rectifier I(Kr), have been found to underlie the congenital Long-QT syndrome, LQT2. LQT2 may give rise to severe arrhythmogenic phenotypes leading to sudden cardiac death.
+
+**OBJECTIVE:** We attempt to elucidate the mechanisms by which heterogeneous LQT2 genotypes can lead to prolongation of the action potential duration (APD) and consequently the QT interval on the ECG.
+
+**METHODS:** We develop Markovian models of wild-type (WT) and mutant I(Kr) channels and incorporate these models into a comprehensive model of the cardiac ventricular cell.
+
+**RESULTS:** Using this virtual transgenic cell model, we describe the effects of HERG mutations on the cardiac ventricular action potential (AP) and provide insight into the mechanism by which each defect results in a net loss of repolarizing current and prolongation of APD.
+
+**CONCLUSIONS:** This study demonstrates which mutations can prolong APD sufficiently to generate early afterdepolarizations (EADs), which may trigger life-threatening arrhythmias. The severity of the phenotype is shown to depend on the specific kinetic changes and how they affect I(Kr) during the time course of the action potential. Clarifying how defects in HERG can lead to impaired cellular electrophysiology can improve our understanding of the link between channel structure and cellular function.
+
+---
+
+[Rudy lab site reference to model](http://rudylab.wustl.edu/research/cell/methodology/markov/clancy_herg.htm)
+
+---
+
+## Model:
+
+```
+C1 <==> C2 <==> C3 <==> O <==> I
+```
+
+IKr = G_Kr * P(O) * (V_m - E_K)
+P(O) = open probability of I_Kr
+G_Kr = 0.0135 * ([K+]_o)^0.59
+E_K = (R*T/F) * ln([K+]_o / [K+]_i)
+
+### Wild-type rate constants
+
+- C1 ==> O or C1 ==> I
+  aa = 65.5e-3 * exp(0.05547153*(v - 36))
+- C2 ==> C1
+  a_in = 2.172
+- C3 ==> C2
+  a = 55.5e-3 * exp(0.05547153*(v - 12))
+- C2 ==> C3
+  b = 2.357e-3 * exp(-0.036588*(v))
+- C1 ==> C2
+  b_in = 1.077
+- O ==> C1
+  bb = 2.9357e-3 * exp(-0.02158*(v))
+- I ==> O
+  ai = 0.439 * exp(-0.02352*(v + 25)) * 4.5 / [K+]_o
+- O ==> I
+  bi = 0.656 * exp(0.000942*(v)) * (4.5 / [K+]_o)^0.3
+- I ==> C1
+  mu = (ai * bb * aa) / (aa * bi)
+
+### T474I rates
+
+- C1 ==> O
+  aa = 65.5e-3 * exp(0.05547153*(v + 25))
+- C3 ==> C2
+  a = 55.5e-3 * exp(0.05547153*(v + 6))
+
+### R56Q rates
+
+- C2 ==> C3
+  b = 2.357e-3 * exp(-0.036588*(v)) * 10.5
+- O ==> C1
+  bb = 2.9357e-3 * exp(-0.02158*(v)) * 6.3
+
+### N629D rates
+
+- O ==> I
+  bi = 0.0
+- N629D loss of selectivity
+
+Na:K permeability (P_Na / P_K) = 0.65
+
+E_K = (R*T/F) * ln([K+]_o + (P_Na / P_K) * [Na+]_o / [K+]_i + (P_Na / P_K) * [Na+]_i)
+
+### Syntax note:
+
+- e-n is 10^-n
+- exp(n) is e^n
+
+---
+
+## To run the models:
+
+XPP: start with the command
+
+```
+xppaut IERG_Mar.ode
+```
+
+Mouse click on Initialconds, and then (G)o.
+This makes a trace similar to fig 4B (0mV) of the paper.
+To obtain the other traces in figure 4B you can press the Param button on the top of the XPP screen. Enter a new vtest (e.g. one of -30, -20, ... 30, 40) and click Go.
+
+To run as a series of voltage-clamp studies, click Range over, change to 'vtest', and then select voltage protocol from Steps (8), Start (-30) and End (40).
+
+Regarding the xpp program, please contact Bard Ermentrout's website [http://www.pitt.edu/~phase/](http://www.pitt.edu/~phase/) which describes how to get and use xpp (Bard wrote xpp).
+
+---
+
+## These model files were submitted by:
+
+Dr. Sheng-Nan Wu, Han-Dong Chang, and Jiun-Shian Wu  
+Dept Physiol  
+Natl Cheng Kung U Med Coll  
+Tainan 70101, Taiwan
+
+snwu@mail.ncku.edu.tw
+
+---
+
+2025-05-27 – Standardized to Markdown