We investigated the role of protein kinase A (PKA) in regulation of the human ether-a-go-go-related gene (HERG) potassium channel activation. HERG clones with single mutations destroying one of four consensus PKA phosphorylation sites (S283A, S890A, T895A, S1137A), as well as one clone carrying all mutations with no PKA phosphorylation sites (HERG 4M) were constructed. These clones were expressed heterologously in Xenopus oocytes, and HERG potassium currents were measured with the two microelectrode voltage clamp technique. Application of the cAMP-specific phosphodiesterase (PDE IV) inhibitor Ro-20 -1724 (100 M), which results in an increased cAMP level and PKA stimulation, induced a reduction of HERG wild type outward currents by 19.1% due to a shift in the activation curve of 12.4 mV. When 100 M Ro-20 -1724 was applied to the HERG 4M channel, missing all PKA sites, there was no significant shift in the activation curve, and the current amplitude was not reduced. Furthermore, the adenylate cyclase activator forskolin that leads to PKA activation (400 M, 60 min), shifted HERG wild type channel activation by 14.1 mV and reduced currents by 39.9%, whereas HERG 4M channels showed only a small shift of 4.3 mV and a weaker current reduction of 22.3%. We conclude that PKA regulates HERG channel activation, and direct phosphorylation of the HERG channel protein has a functional role that may be important in regulation of cardiac repolarization.In cardiac myocytes, repolarization of the action potential is produced by different potassium currents (1). Activation of the rapid component of the delayed rectifier potassium current, I Kr , 1 initiates repolarization and terminates the plateau phase of the cardiac action potential. The human ether-a-go-go-related gene (HERG) (2) encodes the voltage-gated potassium channel underlying I Kr . This has been demonstrated in macroscopic current measurements (3, 4) and single channel measurements (5). HERG channels are one primary target for the pharmacological management of arrhythmias with class III antiarrhythmic drugs: I Kr is blocked and the cardiac action potential is prolonged (5-7). Mutations in HERG produce chromosome 7-linked congenital long QT syndrome (LQT2) (3). These mutations are associated with delayed cardiac repolarization, prolonged electrocardiographic QT intervals (8), and a high risk for the development of ventricular "torsade de pointes" arrhythmias and sudden cardiac death (9).Cyclic AMP-dependent protein kinase (PKA) is a key enzyme for numerous regulatory processes in almost all types of cells. It has been demonstrated that PKA regulates ion channels in native tissue (10). PKA is a serine/threonine kinase that can be stimulated by extracellular signals that elevate intracellular cAMP concentrations. cAMP binds to the regulatory subunit of the enzyme, which leads to dissociation of regulatory and catalytic subunits. The catalytic subunit phosphorylates the substrate at its specific phosphorylation sites. The substrate may either be the effector protein or an...

The human ether-a-go-go-related gene (HERG) encodes a K+ channel with biophysical properties nearly identical to the rapid component of the cardiac-delayed rectifier K+ current (I(Kr)). HERG channels are one primary target for the pharmacological management of arrhythmias. In this study, we investigated the acute effects of the class III antiarrhythmic drug amiodarone on HERG channels expressed heterologously in Xenopus oocytes by use of the two-microelectrode voltage clamp technique. Amiodarone blocked HERG channels with an IC50 of 9.8 microM with a maximum outward tail current reduction of 62.8%. The block consisted of two main components, a closed channel block that could not be reversed within the time of experiments and an open channel block with a slow unblock, having a recovery time constant of 73 s at -80 mV. Inactivation of the HERG channel at very positive potentials could not prevent amiodarone block. These results indicate that HERG channels can be blocked by amiodarone in closed, open and inactivated states. The block of open channels was cumulative, use-dependent and voltage-dependent. In summary, our data suggest that the strong class III antiarrhythmic action of amiodarone is at least partially based upon its acute inhibitory effects on HERG potassium channels.

BackgroundRecent genome-wide association studies have identified several genetic loci linked to coronary artery disease (CAD) and myocardial infarction (MI). The 9p21.3 locus was verified by numerous replication studies to be the first common locus for CAD and MI. In the present study, we investigated whether six single nucleotide polymorphisms (SNP) rs1333049, rs1333040, rs10757274, rs2383206, rs10757278, and rs2383207 representing the 9p21.3 locus were associated with the incidence of an acute MI in patients with the main focus on the familial aggregation of the disease.MethodsThe overall cohort consisted of 976 unrelated male patients presenting with an acute coronary syndrome (ACS) with ST-elevated (STEMI) as well as non-ST-elevated myocardial infarction (NSTEMI). Genotyping data of the investigated SNPs were generated and statistically analyzed in comparison to previously published findings of matchable control cohorts.ResultsStatistical evaluation confirmed a highly significant association of all analyzed SNP's with the occurrence of MI (p < 0.0001; OR: 1.621-2.039). When only MI patients with a positive family disposition were comprised in the analysis a much stronger association of the accordant risk alleles with incident disease was found with odds ratios up to 2.769.ConclusionsThe findings in the present study confirmed a strong association of the 9p21.3 locus with MI particularly in patients with a positive family history thereby, emphasizing the pathogenic relevance of this locus as a common genetic cardiovascular risk factor.

Background-The tachycardia detection interval (TDI) in implantable cardioverter/defibrillators (ICDs) is conventionally programmed according to the slowest documented ventricular tachycardia (VT), with a safety margin of 30 to 60 ms. With this margin, VTs above the TDI may occur. However, longer TDIs are associated with an increased risk of inappropriate therapy. We hypothesized that patients with slow VTs (Ͻ200 bpm) may benefit from a long TDI and a dual-chamber detection algorithm compared with a conventionally programmed single-chamber ICD. Methods and Results-Patients with VTs Ͻ200 bpm were implanted with a dual-chamber ICD that was randomly programmed to a dual-chamber algorithm and a TDI of Ն469 ms or to a single-chamber algorithm with a TDI 30 to 60 ms above the slowest documented VT cycle length and the enhancement criteria of cycle length variation and acceleration. The primary combined end point was the number of all inappropriate therapies, VTs above the TDI, and VTs with significant therapy delay (Ͼ2 minutes). After 6 months, a crossover analysis was performed. Total follow-up was 1 year. One hundred two patients were included in the study. The programmed TDI was 500Ϯ36 ms during the dual-chamber phase and 424Ϯ63 ms during the single-chamber phase. For the primary end point (inappropriate therapies, VTs above the TDI, or VTs with detection delay), a moderate superiority of the dual-chamber mode was found: Mann-Whitney estimatorϭ0.6661; 95% CI, 0.5565 to 0.7758; Pϭ0.0040. Conclusions-Dual-chamber detection with a longer TDI improves VT detection and does not increase the rate of inappropriate therapies despite a considerable increase in tachycardia burden.