BACKGROUND: Many long-QT syndrome (LQTS) mutations in the cardiac Na+ channel result in a gain of function due to a fraction of channels that fail to inactivate (burst), leading to sustained current (Isus) during depolarization. However, some Na+ channel mutations that are causally linked to cardiac arrhythmia do not result in an obvious gain of function as measured using standard patch-clamp techniques. An example presented here, the SCN5A LQTS mutant I1768V, does not act to increase Isus (<0.1% of peak) compared with wild-type (WT) channels. In fact, it is difficult to reconcile the seemingly innocuous kinetic alterations in I1768V as measured during standard protocols under steady-state conditions with the disease phenotype. METHODS AND RESULTS: We developed new experimental approaches based on theoretical analyses to investigate Na+ channel gating under non-equilibrium conditions, which more closely approximate physiological changes in membrane potential that occur during the course of a cardiac action potential. We used this new approach to investigate channel-gating transitions that occur subsequent to channel activation. CONCLUSIONS: Our data suggest an original mechanism for development of LQT-3 arrhythmias. This work demonstrates that a combination of computational and experimental analysis of mutations provides a framework to understand complex mechanisms underlying a range of disorders, from molecular defect to cellular and systems function.
BACKGROUND: Many long-QT syndrome (LQTS) mutations in the cardiac Na+ channel result in a gain of function due to a fraction of channels that fail to inactivate (burst), leading to sustained current (Isus) during depolarization. However, some Na+ channel mutations that are causally linked to cardiac arrhythmia do not result in an obvious gain of function as measured using standard patch-clamp techniques. An example presented here, the SCN5A LQTS mutant I1768V, does not act to increase Isus (<0.1% of peak) compared with wild-type (WT) channels. In fact, it is difficult to reconcile the seemingly innocuous kinetic alterations in I1768V as measured during standard protocols under steady-state conditions with the disease phenotype. METHODS AND RESULTS: We developed new experimental approaches based on theoretical analyses to investigate Na+ channel gating under non-equilibrium conditions, which more closely approximate physiological changes in membrane potential that occur during the course of a cardiac action potential. We used this new approach to investigate channel-gating transitions that occur subsequent to channel activation. CONCLUSIONS: Our data suggest an original mechanism for development of LQT-3arrhythmias. This work demonstrates that a combination of computational and experimental analysis of mutations provides a framework to understand complex mechanisms underlying a range of disorders, from molecular defect to cellular and systems function.
Authors: Ye Chen-Izu; Robin M Shaw; Geoffrey S Pitt; Vladimir Yarov-Yarovoy; Jon T Sack; Hugues Abriel; Richard W Aldrich; Luiz Belardinelli; Mark B Cannell; William A Catterall; Walter J Chazin; Nipavan Chiamvimonvat; Isabelle Deschenes; Eleonora Grandi; Thomas J Hund; Leighton T Izu; Lars S Maier; Victor A Maltsev; Celine Marionneau; Peter J Mohler; Sridharan Rajamani; Randall L Rasmusson; Eric A Sobie; Colleen E Clancy; Donald M Bers Journal: J Physiol Date: 2015-03-15 Impact factor: 5.182