Twitch potentiation by rest in canine ventricular muscle: effects of theophylline.

Short rest of the regular stimulation of the isolated canine right ventricular muscle induced a large transient increase of subsequent twitch tension (rest-twitch potentiation, RTP). This RTP attained the maximum level when the rest period was 120 s and decayed progressively at longer rest periods. The rate of regular stimulation prior to rest affected the degree of RTP but not the time course of RTP. The action potential duration was prolonged progressively after rest until 120 s and maintained this level at longer rest periods. Under the same experimental condition, RTP was not induced in the rabbit papillary muscle. Theophylline, caffeine, and epinephrine increased the strength of steady-state contraction, whereas RTP was inhibited by theophylline and caffeine and unaffected by epinephrine. Manganese and D 600 significantly reduced the strength of steady-state contraction but did not affect the degree of RTP. These results indicate that RTP is induced via a mechanism different from that regulating the steady-state contraction.