Human Molecular Genetics

1. Human Molecular Genetics Disease - cardiac arrhythmia Gene Prediction & Prevention Protein Structure & Function Cell Biology and Physiology Organ Biology and Physiology

8. Ionic Basis of TMAP Depolarization result of net inward current Repolarization result of net outward current Phase 0 - INa, ICa Phase 1 - Ito,other IK, ↓INa,ICa Phase 2 - IKr, IKs, other IK,INa/Ca, ↓INa,ICa Phase 3 - IKr, IKs, other IK,

9. Kv Channels and Long QT 1. Nomenclature Molecular Components Structure Function Background Genetic Disease Genetic Disease Unmasked by Drug Genetic Disease in Setting of Heart Disease

10. TMAP and Equilibrium Potential – Electrochemical Gradient Ca Inward Current Na Inward Current Magnitude of INa determines magnitude and rise time of phase 0 in atrial and ventricular myocytes

12. TMAP – Current Magnitude Ca Inward Current K Outward Currents Na Inward Current Magnitude of K Current Determines AP Duration (APD) Decrease in K currents - ↑ APD Increase in K currents - ↓ APD

13. TMAP – Current Magnitude Ca Inward Current K Outward Currents Na Inward Current Magnitude of K Current Determines APD Decrease in K currents - ↑ APD Increase in K currents - ↓ APD

14. Electrical Activity of the Heart • In a single atrial or ventricular muscle cell phase 0 results from activation of INa (inward). INa depolarizes the cell. • In the intact heart phase 0 results in propagation of impulse throughout the heart. • During phase 0 ICa(inward), IK (outward) are also activated. The increase in ICa leads to Ca2+ influx (plateau) and E-C coupling. The increase in IK leads to repolarization of cells throughout the heart.

15. Response Depends on Resting Potential Cell excited at – 90 mV resting potential results in a large amplitude phase 0 (upstroke) – fast conduction in a multicellular system Cell excited at more positive resting potentials (e.g., - 75 to - 65 mV results in small amplitude phase 0 – slow conduction in a multicellular system Factor that leads to a more positive resting potentials is an elevated extracellular [K+] e.g., myocardial ischemia, renal failure, diabetic ketoacidosis (advanced & poorly controlled diabetes mellitus)

16. Currents INa (inward) largest current basis of phase 0 depolarization in cells in atria, ventricles, His bundle and Purkinje fibers ICa (inward ) small current makes a contribution to shape of phase 2 IK (outward) contributes to phases 2 and 3 IK1 (outward) contributes to terminal part of phase 3 and resting potential

17. Inward Rectifier

18. TMAP and I-V IK1

19. TMAP – Current Magnitude Ca Inward Current K Outward Currents Na Inward Current Magnitude of K Currents Determine APD Decrease in K current IK - ↑ APD Increase in K currents IK - ↓ APD

20. Refractoriness in Heart

21. Schematic of Ionic Currents that Underlie Cardiac Action Potential (Shah et al. Circ Res 112:2517 2005)

22. Pore-forming (a) subunits of cardiac Nav (A) and Kv (B and C) channels linked to inherited arrhythmias Nerbonne, J. M. et al. Physiol. Rev. 85: 1205-1253 2005

23. Summary of Mutations Splawski et al. Circulation 102:1178 2000

24. Loss of Function Mutations Current Gene Phenotype Frequency IKsKCNQ1 LQT1 ~50% KCNE1 LQT5 Rare IKrKCNH2 LQT2 ~30-40% KCNE2 LQT6 Rare IK1Kir2.1 AS,LQT7 Rare

25. Gain of Function Mutations Current Gene Phenotype Frequency IKsKCNQ1 SQTS2, FAF Rare KCNE1 IKrKCNH2 SQTS1 Rare KCNE2 FAF Rare INaSCN5A LQT3 5-10% IK1KCNJ2 SQTS3 Rare ICa,LCACNA1c TS/LQT8

26. Schematic of Ionic Currents that Underlie Cardiac Action Potential (Shah et al. Circ Res 112:2517 2005)

29. Ionic Currents During TMAP Determined by voltage-clamp technique Ionic substitution, pharmacologic blockade, pulse protocols to isolate current of interest H-H analysis of currents Models of currents to simulate measured currents Improvement in amplifiers, experimental preparations, new drugs and toxins provide channel blockade and leave residual current that accurately reflect current from a single type of ion channel