The influence of some cardiodepressant drugs on the histamine-induced restoration of contractility in potassium-depolarized heart preparations.

The ability of some drugs to affect calcium movements in cardiac fibers was tested using a simple method. Guinea-pig ventricular strips were depolarized by 22 mM K+ and their mechanical activity was restored by histamine (10(-5) M); in in these conditions, the effects on contractility of the classic calcium antagonistic drugs nifedipine, verapamil and D600, of the antiarrhythmic drugs lidocaine, quinidine and propafenon, and of a barbiturate, thiopental, were assessed. These drugs were chosen because all of them have been reported as affecting cardiac contractility. It was observed that the ED50 values obtained for the calcium antagonists were in good agreement with those calculated by other authors using different techniques. Moreover, it was found that at high concentrations either the antiarrhythmic drugs or thiopental showed a cardiodepressant activity; the likely explanation of their effects is discussed.