Abstract
A model of calcium movement during activation of frog skeletal muscle
is described. The model was based on the half sarcomere of a myofibril
and included compartments representing the terminal cisternae, the
longitudinal sarcoplasmic reticulum, the extramyofibrillar space,
and the myofibrillar space. The calcium-binding proteins troponin,
parvalbumin, and calsequestrin were present in appropriate locations
and with realistic binding kinetics. During activation a time-dependent
permeability in the terminal cisternal wall led to calcium release
into the myoplasm and its diffusion through the myoplasm longitudinally
and radially was computed. After adjustment of three parameters,
the model produced a myoplasmic free-calcium concentration that was
very similar to those recorded experimentally with calcium indicators.
The model has been used to demonstrate the importance of parvalbumin
in the relaxation of skeletal muscle, to describe the time course
and magnitude of calcium gradients associated with diffusion across
the sarcomere, and to estimate the errors associated with the use
of aequorin as an intracellular calcium indicator in muscle.
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