[Experments on the mechanism of action of vascular spasmolytic agents. I. Effect nitroprusside sodium, nitroglycerine, prenylamine and verapamil on the arrested potassium contracture of isolated coronary arteries].

On the potassium contracture of isolated coronary arteries of cattle, the relaxation effected by calcium depletion can be blocked by lanthanum ions. The contracture persisting in calcium-free solution (arrested potassium contracture) is used to differentiate the sites of attack of spasmolytics. Verapamil and prenylamine are ineffective in this contracture model. By contrast, nitroprusside sodium and nitroglycerol as before act spasmolytically. Thus, both groups of drugs act through basically different sites. The findings are consistent with the hypothesis that the spasmolytic action of verapamil and prenylamine is based on a blockade of calcium influx. For nitroprusside sodium and nitroglycerol such a mechanism on the arrested potassium contracture has to be ruled out.