Effects of dilazep on the electrophysiological properties of rabbit sinoatrial node cells

The electrophysiological effect of dilazep (1 X 10(-7) -3 X 10(-6) M), a coronary vasodilator, was examined on rabbit sinoatrial node cells using glass microelectrode and double microelectrode voltage clamp methods. Dilazep exerted a negative chronotropic effect and decreased the maximum rate of depolarization of the upstroke of the action potential and the amplitude of the action potential. The action potential duration at half-amplitude was prolonged after the drug perfusion. The voltage clamp experiment showed that dilazep reduced the slow inward current (Isi), the potassium outward current (IK), and the hyperpolarization-activated current (Ih). The recovery time constant of Isi was also prolonged. In conclusion, it is indicated that dilazep has no specific effect on the current system, but the drug depresses specifically the electrical activity of sinoatrial node cells.