| Abstract: | The effects of disopyramide on the membrane potentials and currents of rabbit sinus node cells were studied using the conventional microelectrode and voltage clamp methods. Disopyramide (5 and 10 micrograms/m1) produced a negative chronotropic effect, and decreased the maximum rate of depolarization, the overshoot potential and the maximum diastolic potential. The action potential duration at half-amplitude was prolonged, and the slope of diastolic depolarization was reduced. In the voltage clamp experiments, disopyramide (10 and 50 micrograms/m1) reduced the potassium outward current (IK) without changing its kinetics. Disopyramide reduced the slow inward current Isi and increased the recovery time constant of Isi. The hyperpolarization-activated current (Ih) was also decreased by the drug. From these results, it is concluded that disopyramide has a depressant effect on the electrical activity of sinus node cells by mediating depression of IK, Isi and Ih. |
