Protective effect of cycloprotobuxine-A against cardiac arrhythmias induced by ouabain

Cycloprotobuxine-A (CPB-A) 1-4 mg.kg-1 iv increased the dose of ouabain required to induce ventricular arrhythmias in guinea pigs. At the equitoxic doses (1/50 LD50), CPB-A was more potent than cyclovirobuxine-D and amiodarone. Pretreatment with reserpine (5 mg.kg-1 ip), vagotomy or pithing spinal cord did not prevent the action of CPB-A, which indicate that the protective effect of CPB-A may be due to its direct action on myocardium without the involvement of nervous system. In isolated guinea pig ventricular muscles, CPB-A 3 mumol.L-1 consistently decreased the amplitude of oscillatory afterpotentials (OAP) and blocked triggered activity elicited by ouabain. At 30 mumol.L-1, CPB-A abolished the appearance of OAP. It seems that one of the mechanisms for the anti-arrhythmic action of CPB-A was a decrease in the amplitude of OAP.