Adrenergic regulation of the rapid component of delayed rectifier K+ current: Implications for arrhythmogenesis in LQT2 patients
Received 20 December 2008; accepted 25 February 2009. published online 04 March 2009.
Background
KCNH2 gene mutations disrupting rapid component of IK (IKr) underlie type 2 congenital long QT syndrome (LQT2). Startled auditory stimuli are specific symptomatic triggers in LQT2, thus suggesting fast arrhythmogenic mechanism.
Objective
We investigated acute α1A- and cyclic adenosine monophosphate (cAMP)–related β-adrenergic modulation of IKr in HL-1 cardiomyocytes, wild type (WT)– and 2 LQT2-associated mutant Kv11.1 channels (Y43D- and K595E-Kv11.1) reconstituted in Chinese hamster ovary (CHO) cells.
Methods
IKr and Kv11.1 currents were recorded using the whole-cell patch-clamp technique and confocal microscopy of HL-1 cardiomyocytes transfected with green fluorescent protein (GFP)-tagged pleckstrin homology domain of phospholipase C-δ1 visualized fluctuations of membrane phosphatidylinositol 4,5-bisphosphate (PIP2) content.
Results
In HL-1 cardiomyocytes expressing human α1A-adrenoceptor, superfusion with phenylephrine significantly reduced IKr amplitude, shifted current activation to more positive potentials, and accelerated kinetics of deactivation. Confocal images showed a decline of membrane PIP2 content during phenylephrine exposure. Simultaneous application of adenylyl cyclase activator forskolin and phosphodiesterase inhibitor 3-isobutyl-1-methylxantine (IBMX) shifted IKr activation to more negative potentials and decreased tail current amplitudes after depolarizations between +10 and +50 mV. In CHO cells, α1A-adrenoceptor activation downregulated WT-Kv11.1 channels and forskolin/IBMX produced a dual effect. Expressed alone, the Y43D-Kv11.1 or K595E-Kv11.1 channel had no measurable function. However, co-expression of WT-Kv11.1 and each mutant protein evoked currents with loss-of-function alterations but identical to WT-Kv11.1 α1A- and forskolin/IBMX-induced regulation.
Conclusion
Acute adrenergic regulation of at least 2 Kv11.1 mutant channels is preserved as in WT-Kv11.1 and native IKr. Suppression of α1A-adrenoceptor-related transduction might have therapeutic implications in some cases of LQT2.
⁎Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Shiga, Japan
†Department of Cardiology, Graduate School of Medicine, Kyoto University, Kyoto, Japan
‡Department of Physiology, Shiga University of Medical Science, Otsu, Shiga, Japan
Address reprint requests and correspondence: Dr. Minoru Horie, Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan
This study was supported by the Japanese Society for the Promotion of Science, research grant No. 19-07209.
ABSTRACT