THE EFFECTS OF CALCIUM ON ISOLATED ARTHROPOD MUSCLE FIBERS

¹ Department of Zoology, University of Pennsylvania, Philadelphia 4, Pa., and Marine Biological Laboratory, Woods Hole, Massachusetts

1. When isolated single muscle fibers of blue crab, lobster and grasshopper have their cut ends exposed to solutions containing the calcium ion, they show the same effects as do frog muscle fibers; that is to say, they shorten and the protoplasm clots. However, the wave of clotting is faster in grasshopper muscle than it is in frog muscle. The degree of shortening of arthropod muscle fibers is less than that of frog muscle.

2. Evidence indicates that single muscle fibers of the grasshopper are more sensitive to calcium ions than are single fibers of the frog and blue crab.

3. The rate of movement of the protoplasmic clot in invertebrates is relatively rapid during the first minute. However, there is a gradual decrease in this rate after the first minute.

4. The clotting reaction can be prevented in invertebrate muscle fibers. In grasshopper muscle fibers, concentrations of 0.005 M sodium or potassium oxalate are effective in preventing the formation of the protoplasmic clot. Ca-free sea water is in itself sufficient to prevent the formation of the protoplasmic clot in muscle fibers of the blue crab. Once initiated, this clotting reaction in crab muscle cannot be stopped immediately by the application of sodium or potassium oxalate.