Abstract
1. When sartorius muscle was exposed to Ringer's solution to which both 1mM ryanodine and 80mM KCl were added, at 0.1mM ryanodine, a slow ryanodine, a slow ryanodine contracture occurred after a latent period of 20 to 30 minutes, and at 1mM ryanodine, a slow sustained one developed immediately after a phasic KCl-contracture.
2. Ryanodine had no effect on the myofibrillar ATPase activity and on the ATP-induced tension development of single glycerol-extracted muscle fiber.
3. Ryanodine did not inhibit the relaxing activity of effective eluate on myofibrils and that of microsomes on myofibrils or single fiber. The effect of preincubation of the microsomes with ATP was not affected by ryanodine.
4. The relaxed fiber by microsomes and the spontaneously relaxed fiber by further incubation after addition of calcium were not contracted by addition of ryanodine.
5. By ryanodine, the inhibitory effect of calcium on the relaxation of fiber by microsomes was slightly potentiated and the rate of spontaneous recovery was remarkably reduced. On the other hand, even in the presence of ryanodine, the complete relaxation was finally produced.
6. Ryanodine reduced markedly the rate of calcium binding by microsomes, but it had only slight effect on the maximal amount of calcium binding.
7. The duration, the rate and the amount of extra splitting of ATP by addition of calcium were affected by ryanodine, while the basic splitting of ATP was not done.
