Key result
Pilsicainide inhibits peak sodium currents both intra- and extracellularly, suggesting a common binding site.
Why the study?
The mechanisms of sodium current blockade by pilsicainide in cardiac myocytes, including intra- and extracellular effects, were not fully characterized.
Pilsicainide blocks sodium channels in cardiac myocytes via a common binding site regardless of intracellular or extracellular application.
Pilsicainide's common Na-channel binding site clarified in animal myocytes; leaves open translation to human antiarrhythmic therapy.
Using a whole cell clamp technique, the blockade of sodium currents (In.) by pilsicainide, a new antiarrhythmic agent, applied either intracellularly or extracellularly, was studied in single myocytes isolated from guinea pig right ventricle. Pilsicainide applied extracellularly inhibited the peak amplitude of INa in concentration- (from 10-5M to 10-4M) and rate- (from 0.5 Hz to 3.0 Hz) dependent manners. The onset rate of the blockade in INa was almost constant, independent of frequency of stimulus, but higher at high concentration of pilsicainide. The time constant in the recovery phase from INa inactivation remained almost constant (65 to 75 msec) in the range of concentrations used. Similar results were obtained by intracellular application of 10-3M pilsicainide. Pilsicainide applied intracellularly inhibited Ina in a rate-dependent manner. The blocking potency of internally applied pilsicainide almost corresponded to that of external 10-5M pilsicainide. The onset rate of INa inactivation (from 0.098/pulse to 0.130/pulse) and the recovery time constant (77 msec) was similar to those of external 10-5M pilsicainide. These results suggest that pilsicainide, irrespective of intra- or extracellular application, shares a common binding site to block INa in cardiac myocytes.
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Hattori et al. (1992) studied this question. Pilsicainide was evaluated on Blockade of sodium currents (INa). Pilsicainide applied either intra- or extracellularly inhibited the peak amplitude of sodium currents in concentration- and rate-dependent manners, suggesting a common binding site.
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