Inhibition of G protein-coupled and ATP-sensitive potassium currents by 2-methyl-3-(3,5-diiodo-4-carboxymethoxybenzyl) benzofuran (KB130015), an amiodarone derivative

2-Methyl-3-(3,5-diiodo-4-carboxymethoxybenzyl) benzofuran (KB130015; KB), a novel compound derived from amiodarone, has been proposed to have antiarrhythmic properties. Its effect on the G protein-coupled inward rectifying K+ current [I-K(ACh) or I-K(Ado)], ATP-sensitive K+ current [I-K(ATP)], and background inward rectifying current (I-K1) were studied in guinea pig atrial and ventricular myocytes by the whole-cell voltage-clamp technique. Receptor-activated I-K(ACh/Ado), induced in atrial myocytes by the stimulation of either muscarinic or Ado receptors was concentration dependently (IC50 value of approximate to0.6-0.8 muM) inhibited by KB. Receptor-independent guanosine 5'-O-(3-thio)triphosphate-induced and background I-K(ACh), which contributes to the resting conductance of atrial myocytes, were equally sensitive to KB (IC50 value of approximate to0.9 muM). I-K(ATP) induced in atrial myocytes during metabolic inhibition with 2,4-dinitrophenol (DNP) was also suppressed by KB, whereas I-K1 measured in ventricular myocytes was insensitive to the drug (KB less than or equal to50 muM). Although being effective when applied from the outside, intracellular application of KB via the patch pipette affected neither I-K(ACh) nor I-K(ATP). 3,3',5-triodo-L-thyronin, which shares structural groups with KB, did not have an effect on the K+ currents. Consistent with the effects on single myocytes, KB did not depolarize the resting potential but antagonized the shortening of action potential duration by carbamylcholine-chloride or by DNP in multicellular preparations and antagonized the shortening of action potential duration by acetylcholine in single myocytes. It is concluded that KB inhibits I-K(ACh) and I-K(ATP) by direct drug-channel interaction at a site more easily accessible from extracellular side of the membrane.