Fig. 6

Rate of Ca²⁺ release from the SR during muscle fiber depolarization calculated from the myoplasmic Ca²⁺ transients measured experimentally in individual muscle fibers. a Measured Ca²⁺ transients (top) and corresponding calculated time course of rate of Ca²⁺ release from the SR (middle) for voltage clamp depolarizations to indicated membrane potentials (bottom). The rate of Ca²⁺ release reaches an early peak and then declines appreciably during continued depolarization. Reproduced, with modification from ref. [78]. b Time course of recovery of Ca²⁺ release following an initial inactivating pulse, followed at various times by a repeat application of the same pulse. After a lag of about 100 ms, the early peak begins to recover and is fully recovered by 600 ms. However, at 600 ms recovery, the release wave form is still smaller than in the initial pulse and recovers much more slowly, indicating recovery from a second process, which was attributed to recovery from SR Ca²⁺ depletion. Reproduced, with modification from ref. [83]. c Ca²⁺ transients (top) and rate of SR Ca²⁺ release (bottom) calculated from the measured Ca²⁺ time courses for a single action potential or for a train of action potentials. Release in the second and later action potentials is considerably reduced compared to the release in the first action potential. Reproduced, with modification from ref. [79]