Molecular remodeling of Kv4.3 potassium channels in human atrial fibrillation

Introduction: Atrial fibrillation (AF) is associated with important alterat ions in cardiac ion channels that cause shortening and impaired rate adapta tion of atrial repolarization, The mechanisms underlying potassium current remodeling in human AF are not clear. We investigated the effects of AF on the gene expression of the Kv4.3, Kv1.4, and Kv1.5 potassium channel subuni ts and correlated the findings with the transient outward (I-to) and the su stained outward (I-sus or I-Kur) potassium current. Methods and Results: Semiquantitative reverse transcription-polymerase chai n reaction was used to evaluate mRNA expression, and ion currents were stud ied with the patch clamp technique in right atrial appendages from patients in AF and compared with those from patients in stable sinus rhythm (SR). T he presence of AF was associated with a 61% reduction in Kv4.3 mRNA express ion (P < 0.001 vs SR), which was paralleled by a reduction in I-to current densities in this group of patients (i.e., at +50 mV: 7.44 +/- 0.76 pA/pF i n SR and 1.24 +/- 0.28 pA/pF in AF; P < 0.001 vs SR). mRNA levels of Kv1.4 were identical in the two groups. AF did not affect either the gene express ion of Kv1.5 or the current densities of I-sus. Conclusion: Chronic AF in humans reduces I-to by transcriptional down-regul ation of the Kv4.3 potassium channel. Altered gene expression is an importa nt component of the electrical remodeling process and may contribute to rep olarization abnormalities in AF.