Functional Characterization of the Andersen-Tawil Syndrome Associated Mutation (M307I) in KCNJ2

Abstract

Background: Inward rectifier potassium channels play a key role in setting and maintaining the resting membrane potential and regulating excitability in various tissues. Kir2.x subfamily members mediate the cardiac inward rectifier potassium current (IK1). KCNJ2 encodes Kir2.1, pore-forming alpha subunit of cardiac IK1, and the mutations in this gene are associated with type 1 Andersen-Tawil Syndrome (ATS1). The aim of this study was to characterize the electrophysiological features of a Kir2.1 missense mutation, M307I, found previously in a Korean family with ATS. Methods and Results: Site-direct mutagenesis and heterologous expression system was used for functional study. Kir2.1-M307I and Kir2.1 or Kir2.2 wild type (WT) channels were expressed individually and together in HEK293 cells to measure IK1 by voltage clamp. After 24h of incubation, the whole cell patch clamp technique revealed a 100% loss of outward current over the voltage range of −60 mV to −20 mV for Kir2.1-M307I alone and when co-expressed with WT channels (current density at −40 mV was 9.6 ±3.6 pA/pF for Kir2.1-WT and 3.0 ±1.6 pA/pF for Kir2.2-WT, n=4-10, p<0.001). The inward current over the voltage range of −140 mV to −80 mV was also reduced significantly in mutant co-expressed with WT channels. We further tested an action potential (AP) voltage clamp protocol in the HEK293 cells expressed the Kir2.1-WT and Kir2.1-WT co-expressed with Kir2.1-M307I. It shows the Ba2+-sensitive IK1 current was lost during the terminal repolarization and diastolic phase of the AP when the mutation was co-expressed with Kir2.1-WT. Conclusions: M307I is a ATS1-associated, loss-of-function missense mutation in KCNJ2 that mediates a dominant-negative effect on both Kir2.1 and Kir2.2 WT channels. The detailed mechanisms for this effect need further investigation.