Shortening of Actomyosin Threads not Induced by Adenosinetriphosphate

Abstract

Using a modification of Hayashi''s technique for preparation of actomyosin threads, the effect of various agents on the percentage shortening of such threads was studied. Acetyl B methylcholine, alcohol, epinephrine, histamine, KC1, thyronin, thyroxine, and veratridine all induce shortening. This shortening is greatest during the first 2 minutes but proceeds in a leisurely manner up to 15 minutes. Generally the total amount of shortening is less than that induced by ATP. If ATP is added after a 15-minute exposure to some other agent, further shortening occurs which brings the curve to the level of ATP alone. When 1.8 M CaCl2 is the agent in which the thread was suspended, CaCl2 makes the threads capable of considerable stretching before tearing occurs. After exposure to veratridine, threads shorten but when suspended in air with the wieght still attached they stretch. Other agents do not induce this final stretching.