Long QT-Linked HERG Mutations at R531 of the S4 Alter the Gating Properties of Wt-HERG

Abstract

Listen

Translate article

Mutations in the human Ether-a-go-go Related Gene (hERG) are linked to Type 2 Long QT Syndrome (LQT2). LQT2-linked mutations at R531 disrupt a conserved basic residue on the fourth transmembrane segment (S4) of the voltage-sensor. To understand the impact that these mutations have on hERG function, we expressed WT-, R531Q-, or R531W-hERG in HEK293 cells. Since LQT2 follows a dominant-inheritance pattern, we also transfected cells with equal amounts of WT- and R531Q-hERG or WT- and R531W-hERG. The whole-cell patch-clamp technique was used to record hERG current (IhERG). I-V relations were measured by pre-pulsing cells in 10-mV increments to 100mV for 5s, followed by a test-pulse to −50mV for 5s. The peak tail IhERG measured during the test-pulse was plotted as a function of the pre-pulse potential. The data were fit with the Boltzmann equation to calculate the maximal IhERG activation, midpoint potential for maximal activation (V1/2), and slope factor (k). Maximal IhERG was not significantly different among the groups; however, there was an increase in the k and a positive shift in the V1/2 of currents recorded from cells expressing mutant channels compared to those expressing WT-hERG. The voltage-dependence for rates of IhERG deactivation, development of inactivation, and recovery from inactivation were measured by calculating the time constants (τ) associated with IhERG decay for a broad range of test potentials. Cells expressing R531Q- and R531W-hERG exhibited a faster mean τ for IhERG deactivation and recovery from inactivation, but a slower τ for development of inactivation. Cells expressing WT-hERG and R531Q- or R531W-hERG tended to have an intermediate effect on the I-V relations and τ. These data suggest that R531Q- and R531W-hERG produce functional channels with altered gating, which persist in the presence of WT-hERG.