Microscopic mechanisms for long QT syndrome type 1 revealed by single-channel analysis of IKs with S3 domain mutations in KCNQ1

Abstract

Background The slowly activating delayed rectifier current IKs participates in cardiac repolarization, particularly at high heart rates, and mutations in this K+ channel complex underlie long QT syndrome (LQTS) types 1 and 5. Objective The purpose of this study was to determine biophysical mechanisms of LQT1 through single-channel kinetic analysis of IKs carrying LQT1 mutations in the S3 transmembrane region of the pore-forming subunit KCNQ1. Methods We analyzed cell-attached recordings from mammalian cells in which a single active KCNQ1 (wild type or mutant) and KCNE1 complex could be detected. Results The S3 mutants of KCNQ1 studied (D202H, I204F, V205M, and S209F), with the exception of S209F, all led to a reduction in channel activity through distinct kinetic mechanisms. D202H, I204F, and V205M showed decreased open probability (Po) compared with wild type (0.07, 0.04, and 0.12 vs 0.2); increased first latency from 1.66 to >2 seconds at +60 mV (I204F, V205M); variable-to-severe reductions in open dwell times (≥50% in V205M); stabilization of closed states (D202H); and an inability of channels to reach full conductance levels (V205M, I204F). S209F is a kinetic gain-of-function mutation with a high Po (0.40) and long open-state dwell times. Conclusion S3 mutations in KCNQ1 cause diverse kinetic defects in IKs, affecting opening and closing properties, and can account for LQT1 phenotypes.