A novel, potent, and selective inhibitor of cardiac late sodium current suppresses experimental arrhythmias.

Inhibition of cardiac late sodium current (late I(Na)) is a strategy to suppress arrhythmias and sodium-dependent calcium overload associated with myocardial ischemia and heart failure. Current inhibitors of late I(Na) are unselective and can be proarrhythmic. This study introduces GS967 (6-[4-(trifluoromethoxy)phenyl]-3-(trifluoromethyl)-[1,2,4]triazolo[4,3-a]pyridine), a potent and selective inhibitor of late I(Na), and demonstrates its effectiveness to suppress ventricular arrhythmias. The effects of GS967 on rabbit ventricular myocyte ion channel currents and action potentials were determined. Anti-arrhythmic actions of GS967 were characterized in ex vivo and in vivo rabbit models of reduced repolarization reserve and ischemia. GS967 inhibited Anemonia sulcata toxin II (ATX-II)-induced late I(Na) in ventricular myocytes and isolated hearts with IC(50) values of 0.13 and 0.21 µM, respectively. Reduction of peak I(Na) by GS967 was minimal at a holding potential of -120 mV but increased at -80 mV. GS967 did not prolong action potential duration or the QRS interval. GS967 prevented and reversed proarrhythmic effects (afterdepolarizations and torsades de pointes) of the late I(Na) enhancer ATX-II and the I(Kr) inhibitor E-4031 in isolated ventricular myocytes and hearts. GS967 significantly attenuated the proarrhythmic effects of methoxamine+clofilium and suppressed ischemia-induced arrhythmias. GS967 was more potent and effective to reduce late I(Na) and arrhythmias than either flecainide or ranolazine. Results of all studies and assays of binding and activity of GS967 at numerous receptors, transporters, and enzymes indicated that GS967 selectively inhibited late I(Na). In summary, GS967 selectively suppressed late I(Na) and prevented and/or reduced the incidence of experimentally induced arrhythmias in rabbit myocytes and hearts.

High throughput electrophysiology with Xenopus oocytes.

Voltage-clamp techniques are typically used to study the plasma membrane proteins, such as ion channels and transporters that control bioelectrical signals. Many of these proteins have been cloned and can now be studied as potential targets for drug development. The two approaches most commonly used for heterologous expression of cloned ion channels and transporters involve either transfection of the genes into small cells grown in tissue culture or the injection of the genetic material into larger cells. The standard large cells used for the expression of cloned cDNA or synthetic RNA are the egg progenitor cells (oocytes) of the African frog, Xenopus laevis. Until recently, cellular electrophysiology was performed manually by a single operator, one cell at a time. However, methods of high throughput electrophysiology have been developed which are automated and permit data acquisition and analysis from multiple cells in parallel. These methods are breaking a bottleneck in drug discovery, useful in some cases for primary screening as well as for thorough characterization of new drugs. Increasing throughput of high-quality functional data greatly augments the efficiency of academic research and pharmaceutical drug development. Some examples of studies that benefit most from high throughput electrophysiology include pharmaceutical screening of targeted compound libraries, secondary screening of identified compounds for subtype selectivity, screening mutants of ligand-gated channels for changes in receptor function, scanning mutagenesis of protein segments, and mutant-cycle analysis. We describe here the main features and potential applications of OpusXpress, an efficient commercially available system for automated recording from Xenopus oocytes. We show some types of data that have been gathered by this system and review realized and potential applications.