Model is underconstrained. The following variables couldn't be defined: * Ca_i in component cytoplasmic_calcium * J_i in component cytoplasmic_calcium * J_ER in component ER_Ca_release * J_pm in component Ca_extrusion_across_the_plasma_membrane * v_ER in component intraluminal_calcium * k_ER in component intraluminal_calcium * Ca_ER_init in component intraluminal_calcium * v_i in component total_cytoplasmic_Ca_flux * k_i in component total_cytoplasmic_Ca_flux * P_ER in component ER_Ca_release * J_SERCA in component Ca_uptake_by_SR_Ca_ATPase * J_ICa in component total_cytoplasmic_Ca_flux * I_Ca in component total_cytoplasmic_Ca_flux * J_extru in component Ca_extrusion_across_the_plasma_membrane * J_release in component ER_Ca_release * d/dt Ca_i in component cytoplasmic_calcium * d/dt Ca_ER in component intraluminal_calcium