[ Effects of combined use of dofetilide and verapamil on the action potential of papillary muscles in guinea pigs ] .
[ Effects of combined use of dofetilide and verapamil on the action potential of papillary muscles in guinea pigs ] . To test the effects of combined use of dofetilide and verapamil on the action potential of papillary muscles in guinea pigs. ### methods Under the stimulation of different frequencies (0.2, 0.5, 1.0, 1.25 or 2.0 Hz), the action potential of papillary muscles in guinea pigs was recorded with the standard microelectrode techniques. The impacts of different concentrations of amiodarone (1, 5 or 10 micromol/L), dofetilide (10, 50, 100 nmol/L), and a combination of 100 nmol/L dofetilide and 1 micromol/L verapamil on the action potential were tested. ### results amiodarone prolonged the action potential duration (APD) significantly, measured both at 50% (APD50) and 90% (APD90) of repolarization, in a concentration-dependent manner independent from stimulation frequencies. dofetilide prolonged APD in a concentration-dependent manner, which was negatively dependent on stimulation frequencies. The frequency-dependent effect was ameliorated by adding 1 micromol/L verapamil to dofetilide. ### conclusion Both amiodarone and dofetilide prolong APD in a concentration-dependent manner. The class III antiarrhythmic compounds, amiodarone, has less frequency-dependent effect than the pure class III antiarrhythmic drug. A combined use of potassium and calcium antagonists may reduce the frequency-dependence of the pure class III antiarrhythmic drug.
### Instruction:
            Given the context about compound efficacy for the given treatment mentioned within the input, mentioned the compounds 
            that can co-occur for the mentioned treatment

            ### Input:
            [ Effects of combined use of dofetilide and verapamil on the action potential of papillary muscles in guinea pigs ] . To test the effects of combined use of dofetilide and verapamil on the action potential of papillary muscles in guinea pigs. ### methods Under the stimulation of different frequencies (0.2, 0.5, 1.0, 1.25 or 2.0 Hz), the action potential of papillary muscles in guinea pigs was recorded with the standard microelectrode techniques. The impacts of different concentrations of amiodarone (1, 5 or 10 micromol/L), dofetilide (10, 50, 100 nmol/L), and a combination of 100 nmol/L dofetilide and 1 micromol/L verapamil on the action potential were tested. ### results amiodarone prolonged the action potential duration (APD) significantly, measured both at 50% (APD50) and 90% (APD90) of repolarization, in a concentration-dependent manner independent from stimulation frequencies. dofetilide prolonged APD in a concentration-dependent manner, which was negatively dependent on stimulation frequencies. The frequency-dependent effect was ameliorated by adding 1 micromol/L verapamil to dofetilide. ### conclusion Both amiodarone and dofetilide prolong APD in a concentration-dependent manner. The class III antiarrhythmic compounds, amiodarone, has less frequency-dependent effect than the pure class III antiarrhythmic drug. A combined use of potassium and calcium antagonists may reduce the frequency-dependence of the pure class III antiarrhythmic drug.

            ### Response:
            dofetilide, verapamil
            