Caffeine contracture in frog cardiac muscle after exposure to high concentrations of calcium.

Caffeine induced contracture in frog auricular muscle at room temperature when the muscle was exposed to a Ca-rich solution. The initial transient tension lasted 10-30 sec, and it was inhibited by procaine. It was dependent on caffeine concentration and the time of exposure to a Ca-rich solution prior to caffeine attack, but was little dependent on Ca concentration during caffeine contracture.