Group 3 Stony Brook University BME 301 Long QT Syndrome Type 2 (LQT2) Scott Dow, Hui Zheng, Mohammad Reda El Mkhantar, Kamal James Monjur Khuda, Hanbei Zhang, Dandi Zheng, Anders Chan

Long QT Syndrome (LQTS) Comprises a number of disorders, all of which involve an elongated QT interval In this case, caused by delayed ventricular repolarization Not a problem per se, but is a risk factor for more dangerous complications, such as ventricular arrhythmias

LQT2 Syndrome A specific type of LQTS caused by mutations of HERG gene, which codes for Kv11.1, the α-subunit that makes up the pores of Ikr channels

Ikr Channels & Kv11.1 Ikr is notable for its slow activation/deactivation, and fast inactivation/recovery Kv11.1 is the α-subunit of Ikr The Ikr channel consists of 4 identical α-subunits that together form the pore Each α-subunit comprises 6 transmembrane α helices labeled S1-S6 S4 is most important domain for voltage sensing (+AA every ~3 residues)

Comparing Missense Mutations in hERG Depending on the region affected, mutations can be pathological or benign Most likely harmful mutations are the ones on transmembrane/linker/pore region Mutations may also be nonsense, but these usually never leave the ER *N-terminus, Transmembrane/Linker/Pore, and C-Terminus Domains

Refresher on the Cardiac AP 0. INa depolarizes the cell 1. Ito sets the plateau voltage 2. ICa-L & IKs balance to create a the plateau 3. IKr, IKs, and IK1 repolarize 4. Ik1 enforces negative Vm Sherwood, L. (2012). Human Physiology, From Cells to Systems (8th [revised] ed.). Cengage Learning. ISBN 9781111577438.

What kinds of loss in function? Reduction in number of channels in the cell membrane (changes effective gkr) Due to reduced protein trafficking since quality control mechanisms prevent departure from ER Decreasing single channel conductance Pore forming domains are mutated Changing probability of channel gates to be open E.g. Deactivation can be accelerated by N or C-terminal mutations (these help regulate gating)

Reduced Ikr Conductance - So What? Reduction in gkr means a reduction in current With a reduction in Ikr, the slope of phase 3 of the AP is drastically reduced If repolarization is too slow (i.e. delayed)… EADs are possible!!!

What about Altered Gating? Mutations affecting the function of either one of these gates could affect Ikr in numerous ways, including these that we found in the literature: Accelerated deactivation Voltage-shifted inactivation Voltage-shifted activation Any of these can also lead to EADs! Recall that Two Things Characterize Ikr: Slow activation and deactivation Fast inactivation and recovery from inactivation

Early Afterdepolarizations Any depolarization that happens too early and interrupts another AP phase Can be caused by delayed repolarization as in LQT2 (slope not steep enough) Calcium channels have a limited refractory period - if repolarization is delayed, they can fire again or even create a self-sustaining wave Ventricular tachyarrhythmias!!!

MATLAB Code Manipulations Input parameters Ik splitting and scaling factor in Ikr conductance(g_krscale)

MATLAB Code Manipulations Cont’d Voltage shift in activation (vshift_a) and scaling factor in deactivation (Bp) Voltage shift in inactivation (vshift_n)

Effect of gkr Changes on AP

Effects of Voltage Shifting Gates on AP

Effect of Accelerated Deactivation

Member contributions Website: http://you.stonybrook.edu/bmeswagyolo/ Research/Background MATLAB code PPT presentation Website Hui Zheng 1 Scott Dow (presenter) Hanbei Zhang Reda El Mkhantar Kamal James Dandi Zheng Monjur Khuda (presenter) Anders Chan Website: http://you.stonybrook.edu/bmeswagyolo/

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