Published Online
on August 25, 2009

A more recent version of this article appeared on October 1, 2009

This Article Full Text (PDF) All Versions of this Article: 2/5/540    most recent CIRCEP.109.872309v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Google Scholar Articles by Vega, A. L. Articles by Makielski, J. C. PubMed PubMed Citation Articles by Vega, A. L. Articles by Makielski, J. C. Related Collections Arrhythmias, clinical electrophysiology, drugs Clinical genetics Arrythmias-basic studies Functional genomics Ion channels/membrane transport

Original Article

PKA-Dependent Biophysical Phenotype for V227F-KCNJ2 Mutation in Catecholaminergic Polymorphic Ventricular Tachycardia

Amanda L. Vega¹; David J. Tester²; Michael J. Ackerman² and Jonathan C. Makielski^3,4

¹ University of Wisconsin, Madison, WI & University of Washington, Seattle, WA;
² Mayo Clinic, Rochester, MN;
³ University of Wisconsin, Madison, WI

^* Corresponding author; email: jcm{at}medicine.wisc.edu

Background—KCNJ2 encodes Kir2.1, a pore-forming subunit of the cardiac inward rectifier current, I_K1. 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 I_K1 by voltage clamp. Unlike typical ATS-associated KCNJ2 mutations which show dominant negative loss of function, Kir2.1WT+V227F co-expression yielded I_K1 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 I_K1 compared to Kir2.1-WT. PKA-induced reduction in I_K1 was eliminated by mutating the phosphorylation site at serine 425 (S425N).

Conclusions—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 I_K1 dysfunction for this KCNJ2 mutation which correlates with adrenergic conditions underlying the clinical arrhythmia.

Key Words: arrhythmia • catecholamines • ion channels • long-QT syndrome • tachycardia • K-channel • Andersen-Tawil syndrome • catecholaminergic polymorphic ventricular tachycardia