抄録
1. Both the rate and the amount of calcium uptake by the reticulum isolated from frog skeletal muscle were dependent on temperature. The activation energy of calcium uptake was about 3, 600cal/mole. A portion of calcium taken up by the reticulum at 20°C was released reversibly by cooling; about 20 and 50mμ moles Ca/mg protein by cooling to 10 and 0°C, respectively.
2. Ten mM caffeine did inhibit the calcium uptake of the reticulum at 20 and 10°C. The inhibitory action of caffeine at 10°C was slightly more remarkable than that at 20°C. It was noted that the calcium uptake at 0°C was not affected by 10mM caffeine.
3. At 20°C, about 20-25mμ moles Ca/mg protein was released from the reticulum by the addition of 1-2mM caffeine. The calcium release induced by 1mM caffeine was only slightly potentiated by cooling from 20 to 10°C. On the other hand, the calcium release by cooling from 20 to 0°C was the same with or without 2mM caffeine present.
4. The calcium taken up by the reticulum at 0°C was only a little released by the addition of 10mM caffeine.
5. The myofibrillar ATPase activity and its Ca-sensitivity were dependent on temperature. The maximal ATPase activity of myofibrils at 10 and 0°C was only about 40 and 6% of that at 20°C, respectively. And the added Ca++ concentration required for half-maximal ATPase activity was about 35μM at 20°C and about 100μM at 10°C, respectively.
6. These results were discussed in relation to the mechanism of rapid cooling contracture in caffeinized frog muscle fiber.
