Effect of trapidil on mechanical and electrical activity of isolated rabbit atrium

Actions of trapidil on mechanical and electrical activities of rabbit right atria were investigated in vitro. Isolated atria had spontaneous contractions. Ca++ (2.7-4.5 mM) concentration-dependently increased force and frequency of atrial contractions, and trapidil (10(-5)-10(-4) g/ml) also did. Trapidil (10(-5)-10(-4) g/ml) showed a tendency to augment the positive inotropic action of Ca++ and significantly enhanced the positive chronotropic action of Ca++. In experiments using conventional microelectrode techniques, trapidil (10(-5)-10(-4) g/ml) concentration-dependently increased the slope of slow diastolic depolarization, the maximal diastolic potentials and the peak potentials in pacemaker potentials of sinoatrial nodal cells, and shortened the cycle length of them. The results indicate pharmacodynamically and electrophysiologically that trapidil produces a positive inotropic and chronotropic effect on isolated rabbit right atria.