Mechanics of manganese ions-induced contraction of ileal longitudinal muscle in Ca(2+)-free, high-K+ medium.

1. Mn2+ (5 mM) evoked the contraction of ileal longitudinal muscle in a Ca(2+)-free, high-K+ (60 mM) medium. Metabolic inhibitors, such as iodoacetic acid or glucose removal, reduced the contraction by Mn2+ in the Ca(2+)-free, high-K+ medium, suggesting that the contraction by Mn2+ depends on energy metabolism. 2. By the abrupt decrease in length of the ileum during contraction 3 hr after the addition of 5 mM Mn2+ in Ca(2+)-free, high-K+ medium, a rapid decrease in tension was seen, and redevelopment of tension followed, which is indicative of an active state. 3. In the late phase, 5 hr after the Mn(2+)-induced contraction, a similar decrease in the length also caused a rapid decrease in tension, without however, a redevelopment of tension. This probably indicates that the myofilaments in this phase transferred to a state of static interaction.