Effects of vasoactive drugs on fluoride-induced contractions of vascular smooth muscle in calcium-free solution.

Cumulative dose-response curves were obtained for contractions induced by fluoride in bovine facial veins and arteries in the presence and absence of external Ca (Cao). In 1.4 mmol/l Cao the threshold for contractions was lower for veins than for the arteries, i.e. at 1 mmol/l vs. 2 mmol/l F-. After Ca withdrawal from the external medium, the ED50 values for veins and arteries were shifted from 2.2 to 10 and from 4.5 and 8.5 mmol/l F-, respectively. Several vasodilators (order of potency to relax veins: caffeine less than verapamil less than sulmazole less than sodium nitroprusside less than papaverine) were investigated for their ability to inhibit contractions induced by F- in Ca2+-free solution. None of them was able to counteract F- induced contractions in Ca2+-free solutions. Furosemide and beta-methyldigoxine were also ineffective. However, nitroprusside, sulmazole and papaverine were able to relax strips pretreated with Ca2+-free solutions. By contrast, contractions of depolarized veins induced by F- in Ca2+-free solutions were significantly, though transiently, inhibited by 10 mmol/l ammonium ions. The vasodilators tested in this study seem thus to act by inhibiting Ca influx at some level of the membrane, while F- may act by mobilizing Ca ions from some unidentified, cellular pools not accessible to the drugs tested in this study.