The effects of the antiarrhythmic drug propafenone at c-type kv1.4 channels in Xenopus laevis oocytes were studied with the two-electrode voltage-clamp technique. Defolliculated oocytes (stage V-VI) were injected with transcribed cRNAs of ferret Kv1.4 Delta N channels. During recording, oocytes were continuously perfused with control solution or propafenone. Propafenone decreased the currents during voltage steps. The block was voltage-, use-, and concentration- dependent manners. The block was increased with positive going potentials. The voltage dependence of block could be fitted with the sum of monoexponential and a linear function. Propafenone accelerated the inactivate of current during the voltage step. The concentration of half-maximal block (IC(50)) was 121 microM/L. With high, normal, and low extracellular potassium concentrations, the changes of IC(50) value had no significant statistical differences. The block of propafenone was PH- dependent in high-, normal- and low- extracellular potassium concentrations. Acidification of the extracellular solution to PH 6.0 increased the IC(50) values to 463 microM/L, alkalization to PH 8.0 reduced it to 58 microM/L. The results suggest that propafenone blocks the Kv1.4 Delta N channel in the open state and give some hints for an intracellular site of action.
Keywords: Anti-arrhythmic drug; Ion Channels, Voltage-Gated; Membrane Currents; Potassium Channels; Voltage Clamp.