Two Compartment Calcium

Let [Ca²⁺]ⁱ represent calcium in the cytoplasm that binds to the thin filament, and [Ca⁺²]^o representrepresents sarcoplasmic reticulum calcium. Then the rate of change of calcium between these two compartments can be described by the following system of ODEs:

k_leak: The rate of constant flow of calcium from the sarcoplasmic reticulum to the cytoplasm.
act: Either 1 or 0 representing status of muscle activation.
k_act: The rate at which calcium enters the cytoplasm due to activation.
k_serca: The rate at which the serca pump removes calcium from the cytoplasm.

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