INVOLVEMENT OF CALCIUM IN THE CARDIAC DEPRESSANT ACTIONS OF A GARLIC DIALYSATE

In order to elucidate a possible role for calcium on the negative card iotropic effects of a garlic (Allium sativum L., Liliaceae) dialysate in rat atria we studied: (a) the effects of our extract 15 min after p reincubation with high and low concentrations of extracellular calcium ([Ca-2+](o)) on left and right activity of rat atria. The negative in otropism of garlic dialysate increased with calcium 0.75 mM; in contra st, high level of calcium (4.5 mM) induced a significant reduction of this depressant effect. None of these treatments modified the negative chronotropism of garlic; (b) nifedipine (10(-9) to 10(-7) M), verapam il (10(-9) to 10(-7) M) and diltiazem (10(-9) to 10(-7) M) induced a c oncentration-dependent synergism of the log concentration-effect curve of garlic dialysate on left atria. Verapamil and diltiazem (10(-7) M) , but not nifedipine increased the inhibitory chronotropism of garlic in right atria; (c) negative inotropic and chronotropic effects demons trated by nifedipine (1 x 10(-10) to 1.1 x 10(-6) M) were antagonized as expected by preincubation with Bay K-8644. Depressant actions of ga rlic were not modified with this pretreatment. These results suggest t hat the negative inotropic effect of our garlic dialysate is related t o [Ca2+](o) availability. It is possible that a restriction of intrace llular calcium contributes to this effect. However, the negative chron otropic effect of garlic is scarcely affected by these modifications. Copyright (C) 1997 Elsevier Science Ireland Ltd.