[Calcium-antagonism, a new principle in coronary vasodilation]

As in all other vessels, coronary contractile tone depends on the availability of Ca ions. Thus, Ca-antagonistic drugs such as verapamil, prenylamine or nifedipine produce a loss of muscle tone in depolarized coronary strips. One molecule of these compounds successfully blocks the action of thousands of Ca ions in excitation-contraction coupling. Nitroglycerine and other nitrites exert a similar action, though in their case relaxation is more rapid, incomplete and spontaneously reversible. In analogy to their well-known Ca-synergistic action on heart muscle fibres, cardiac glycosides are also capable of increasing the coronary vascular tone even in very low concentrations. If, however, suitable doses of Ca-antagonistic compounds are simultaneously administered, the hearts are protected against this unpleasant coronary side effect without an appreciable loss of the inotropic glycoside action on the myocardium.