Effect of scopolamine on action potential of myocardial cell of guinea pig

Action potential of myocardial cell of isolated ventricular septum was recorded by intracellular capillary glass electrode. The duration of action potential (APD) was prolonged from 91±31 ms and 142±39 ms to 115±35 ms and 179±50 ms for APD50 and APD100, respectively by scopolamine 50 μg/ml (p<0.001). The postrepolarization refractory period (PRP) was prolonged greatly from 154±40 ms to 222±80 ms, and the ratio of PRP to APD was increased from 1.6±0.4 to 2.2±0.5 for APD50 30 min after scopolamine. The spontaneous actibity of cardiac cell was decreased from 146±32 beats/min to 92±42 beats/min(30 min). The effects of scopolamine on APD did not show up when theβ-receptors had been blocked by propranolol and the α-receptors had been activated by methoxamine. Scopolamine is supposed to block the reentry excitation by increasing the pacemaker by decreasing the spontaneous activity.