Background-Genetic predisposition is believed to be responsible for most clinically significant arrhythmias; however, suitable genetic animal models to study disease mechanisms and evaluate new treatment strategies are largely lacking. Methods and Results-In search of suitable arrhythmia models, we isolated the zebrafish mutation reggae (reg), which displays clinical features of the malignant human short-QT syndrome such as accelerated cardiac repolarization accompanied by cardiac fibrillation. By positional cloning, we identified the reg mutation that resides within the voltage sensor of the zebrafish ether-à-go-go-related gene (zERG) potassium channel. The mutation causes premature zERG channel activation and defective inactivation, which results in shortened action potential duration and accelerated cardiac repolarization. Genetic and pharmacological inhibition of zERG rescues recessive reg mutant embryos, which confirms the gain-of-function effect of the reg mutation on zERG channel function in vivo. Accordingly, QT intervals in ECGs from heterozygous and homozygous reg mutant adult zebrafish are considerably shorter than in wild-type zebrafish. Conclusions-With

In addition to the known effects of PKA and cAMP, HERG channels are also modulated by PKC. The molecular mechanisms of this PKC-dependent process are not completely understood but do not depend on direct PKC-dependent phosphorylation of the channel.

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...