Abstract
1. Isolated smooth muscle strip from rabbit intestine was used for measuring the isometric tension to observe the effect of adrenaline on the depolarized smooth muscle.
2. Under normal condition, adrenaline causes the relaxation, but by increasing the concentration of K in Krebs solution, this relaxing effect became gradually less, until the effect of adrenaline was reverse. This reversal was obtained only in a narrow range of K concentration.
3. In solution of higher concentration of K, adrenaline caused the relaxation again.
4. Similar stimulant action of adrenaline was observed in muscle strip which has been immersed in NaBr-, TEACl-, LiCl- or choline-Krebs solutions.
5. It is suggested from these results that, as far as mechanical response of smooth muscle is concerned, adrenaline has a single action and the direction of response to adrenaline is determined by the functional condition of the muscle cell membrane.
This work was aided by the Grant (GA BMR 5693) from the Rockefeller Foundation to one of the authors (T. Suzuki).
