Inactivation of calcium release from the sarcoplasmic reticulum in frog skeletal muscle.

摘要: 1. The rate of calcium release (Rrel) from the sarcoplasmic reticulum (SR) in voltage clamped segments frog skeletal muscle fibres was calculated myoplasmic free transients (delta[Ca2+]) measured with indicator dye Antipyrylazo III. 2. During a 100-200 ms depolarizing pulse Rrel reached an early peak and then declined markedly. time course extent decline were independent membrane potential over range potentials where activation varied severalfold. 3. For test pulses applied shortly after relatively large or long conditioning completely lacked peak. gradually recovered as interval between increased to 1 s. 4. A latency often observed before start recovery Rrel. appeared be correlated for delta[Ca2+] fall below certain level, indicating that might represent reversal calcium-dependent process. It therefore proposed rapid during due inactivation SR channels. 5. Inactivation continued develop 20 later. This expected because elevated [Ca2+] pulses. not external potential-dependent inactivation. 6. Small steady elevations small 200 produced marked Rrel, apparent dissociation constant only slightly above resting [Ca2+]. 7. All observations could well simulated by two-step model which equilibrates rapidly high-affinity receptor on channel calcium-receptor complex undergoes slower conformational change inactivated state channel. 8. An alternative binds soluble (e.g. calmodulin) directly inactivates shown formally identical preceding model. Either closely simulate all observations.