Abstract

Studies have been made of the effect of the highly toxic plant alkaloid, ryanodine, on the isotonic contraction of the cat tibialis aniticus muscle preparation in situ. Small intraarterial injections (50 microgm.) of this alkaloid produce a sustained contracture and rigor of the directly and indirectly stimulated muscle. The ryanodine contracture is abolished or arrested by agents which directly or indirectly diminish the activity of the muscle. Conversely, the contracture is accelerated by agents which directly or indirectly increase the activity of the muscle. In addition, agents which produce anoxia of the muscle and those which have as their own property that of producing a contracture, facilitate the action of ryanodine. Finally ryanodine provides a new and useful experimental tool for the problems concerned with the contraction and relaxation of muscle.