IM: To study the direct effect of enalapril on cellular electrophysiology of myocardium. METHODS: Conventional microelectrodes
technique was used to record the
action potentials (AP) of guinea pig
papillary muscles. RESULTS: Enalapril caused an increase of the AP amplitude (APA) and the resting potential (RP) in a concentration dependent manner without any significant change of AP duration, V max and overshoot of AP. Superfusion of ouabain 0 5 μmol·L -1 reduced APA and RP, induced stable delayed after depolarizations (DAD) at different basic cycle lengths (BCL) in a frequency dependent manner. At BCL 200 ms, the amplitude of DAD was large enough to induce nonsustained triggered activity (TA). In additional presence of enalapril 10 μmol·L -1 , the DAD amplitude at 500, 400, 300, and 200 ms were decreased from 5 3±2 3, 5 9±2 8, 7 4±2 1, and 8 9±1 3 to 2 6±0 7, 3 1±1 0, 3 7±1 5, and 5 3±1 1 (mV) respectively, all P <0 01. The compensation intervals were increased in a similar frequency dependent manner. The number of TA induced at BCL 200 ms was decreased from 3 6±0 7 to 0 8±0 2 ( P <0 05). CONCLUSION: Enalapril directly inhibits DAD and TA induced by ouabain through increasing RP and APA, which may contribute to its anti arrhythmic effect.