The effect of caffeine and quinine on calcium efflux and cyclic AMP levels in bovine ileal smooth muscle

1. Quinine (5 mM), and to a lesser extent caffeine (10 mM), cause stimulation of calcium efflux from a resting bovine ileal smooth muscle preparation. 2. Both caffeine and quinine cause a depression in the 100 mM KCl stimulated efflux of a bovine ileal preparation. 3. Caffeine, a methylxanthine, causes a large increase in the level of cyclic AMP in bovine ileal smooth muscle. 4. Quinine, an indole cinchona, has no significant effect on cyclic AMP levels. 5. These results suggest that caffeine and quinine may act at two entirely different calcium components of the excitation-contraction coupling process.