Negative Inotropic Effects of Class I Antiarrhythmics on Guinea Pig Ventricular Myocardium: Correlation with L-Type Ca2+ Channel Blockade

The negative inotropic effects of nine Vaughan Williams class I antiarrhythmic drugs were examined in guinea pig ventricular tissue preparations. The drugs decreased the contractile force of papillary muscles with different potencies: the potency order was propafenone > aprindine > cibenzoline > flecainide > ranolazine > disopyramide > pilsicainide > mexiletine > GS-458967. The potency of drugs correlated with the reported IC50 values to block the L-type Ca2+ channel rather than the Na+ channel. The effects of drugs were roughly the same when examined under a high extracellular K+ solution, which inactivates the Na+ channel. Furthermore, the attenuation of the extracellular Ca2+-induced positive inotropy was strong with propafenone, moderate with cibenzoline, and weak with pilsicainide. These results indicate that the negative inotropic effects of class I antiarrhythmic drugs can be largely explained by their blockade of the L-type Ca2+ channel.

Automated summary

This study examined the negative inotropic effects of nine Vaughan Williams class I antiarrhythmic drugs on guinea pig ventricular tissue. The potency of the drugs to decrease contractile force correlated with their reported IC50 values to block the L-type Ca2+ channel rather than the Na+ channel. The effects of the drugs were similar under a high extracellular K+ solution, indicating that the negative inotropic effects can be largely explained by the blockade of the L-type Ca2+ channel.