Repetitive caffeine contractions in single crayfish muscle fibers

Crayfish muscle fiber responded to 1-4 mM caffeine with repetitive contractions. At 4 mM caffeine, two to four peaks with intervals of 2-3 sec were observed in the tension curve. At 2 mM caffeine, the intervals were prolonged so that the second contraction started after the first contraction ceased. The tension in the second contraction was slower and smaller than the first one. At 1 mM caffeine, very small tensions developed repetitively at intervals of about 1 min and lasted for more than an hour. The time courses of these caffeine contractions were not modified by the current flow in the direction of hyperpolarizing a major part of the muscle membrane. It was observed under a microscope that the contraction in caffeine solution was induced asynchronously. Moreover, repetitive contractions occurred at several sites and propagated in the longitudinal direction of the muscle fiber. The propagation velocities of contraction waves were between 330 and 40 mum/sec depending on the time after perfusion with caffeine solution.