EFFECT OF CALCIUM, STRONTIUM AND MAGNESIUM ON THE POSITIVE INOTROPIC ACTION OF FLUORIDE

¹ Department of Pharmacology, University of Southern California School of Medicine, Los Angeles, California

The effects of fluoride on the frequency-force relations of rat ventricle strips were studied. Fluoride stimulated the basal contractions. The effect on the first poststimulation contraction was biphasic; it was stimulated and then depres. sed. The positive inotropic effect was greater when the tissue was exposed to fluoride in the presence of calcium, strontium or magnesium than in the absecnce of these ions. Fluoride potentiated the effect of calcium on the basal contractions and antagonized the effect of increasing calcium concentration on the first poststimulation contraction. These results suggest that fluoride exerts its effects as a complex, and its effect on contractility is not simply an increased sensitivity of the tissue to calcium.