KCNJ2 encodes Kir2.1, a pore-forming subunit of the cardiac inward rectifier current, IK1. KCNJ2 mutations are associated with Andersen-Tawil syndrome (ATS) and also Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT). The aim of this study was to characterize the biophysical and cellular phenotype of a KCNJ2 missense mutation, V227F, found in a patient with CPVT.
Methods and Results
Kir2.1-wild type (WT) and V227F channels were expressed individually and together in Cos-1 cells to measure IK1 by voltage clamp. Unlike typical ATS-associated KCNJ2 mutations which show dominant negative loss of function, Kir2.1WT+V227F co-expression yielded IK1 indistinguishable from Kir2.1-WT under basal conditions. To simulate catecholamine activity, a PKA-stimulating cocktail comprised of forskolin and 3-isobutyl-1-methylxanthine (IBMX) was used to increase PKA activity. This PKA-simulated catecholaminergic stimulation caused marked reduction of outward IK1 compared to Kir2.1-WT. PKA-induced reduction in IK1 was eliminated by mutating the phosphorylation site at serine 425 (S425N).
Heteromeric Kir2.1-V227F and WT channels showed an unusual latent loss of function biophysical phenotype that depended upon PKA-dependent Kir2.1 phosphorylation. This biophysical phenotype, distinct from typical ATS mutations, suggests a specific mechanism for PKA dependent IK1 dysfunction for this KCNJ2 mutation which correlates with adrenergic conditions underlying the clinical arrhythmia.
Keywords: K-channel, arrhythmia (mechanisms), long QT syndrome, Andersen-Tawil syndrome, catecholaminergic polymorphic ventricular tachycardia