ryanodine and amentoflavone

Amentoflavone, like caffeine, caused a concentration-dependent increase in Ca2+ release from the heavy fraction of fragmented sarcoplasmic reticulum of rabbit skeletal muscle. The Ca2+ -releasing activity of amentoflavone was approximately 20 times more potent than that of caffeine. The bell-shaped profile of Ca2+ dependence for amentoflavone was almost the same as that for caffeine. Typical blockers of Ca2+ -induced Ca2+ release channels, such as Mg2+, procaine and ruthenium red, inhibited markedly amentoflavone- and caffeine-induced 45Ca2+ release. The maximum 45Ca2+ release in response to amentoflavone was not changed by caffeine, but was further increased by adenosine-5'-(beta,gamma-methylene) triphosphate. This compound enhanced [3H]ryanodine binding to the heavy fraction of fragmented sarcoplasmic reticulum with a decrease in K(D) but without a change in Bmax. These results suggest that amentoflavone, which does not contain a nitrogen atom, probably binds to the caffeine-binding site in Ca2+ channels and thus potentiates Ca2+ -induced Ca2+ release from the heavy fraction of fragmented sarcoplasmic reticulum.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Biflavonoids; Binding, Competitive; Caffeine; Calcium; Electrodes; Flavonoids; Muscle, Skeletal; Rabbits; Ryanodine; Sarcoplasmic Reticulum; Tritium