Electrophysiological effects of bisaramil-a new antiarrhythmic drug under clinical trial-were investigated on isolated heart preparations, at a concentration range of 2.3-23×10-6 m. Bisaramil dose dependently decreased the maximum rate of depolarization (Vmax), action potential amplitude (APA) and overshoot (OS) both in auricle and in papillary muscle of guinea-pig heart. There was no significant and obvious effect on the duration of the action potential and the resting membrane potential was also unchanged. Bisaramil slowed the spontaneous frequency of pacemaker cells in rabbit sinus node preparation due to its inhibitory effect on slow diastolic depolarization (SDD). Bisaramil was able to inhibit slow Ca2+-action potentials induced by isoprenaline on K+-depolarized papillary muscle. Results obtained with transmembrane current measurements revealed that bisaramil inhibited both fast Na+-current and slow Ca2+-current in frog sinoauricular fibres at the same concentration. Bisaramil with a mixed mode of the action seems to be a very promising drug.
- 'slow Ca-action potential'
- pacemaker type action potential
- transmembrane action potential
- transmembrane ionic currents
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