Model is underconstrained.
The following variables couldn't be defined:
 * Istim in component stimulus_protocol
 * i_Na in component sodium_current
 * i_K in component potassium_current
 * i_leak in component leak_current
 * x_infinity in component sodium_current
 * n in component potassium_current_n_gate
 * alpha_x in component sodium_current
 * beta_x in component sodium_current
 * alpha_n in component potassium_current_n_gate
 * beta_n in component potassium_current_n_gate
 * Ca in component calcium_concentration
 * T in component transmitter_release
 * Ca_open in component calcium_concentration
 * sigma in component calcium_concentration
 * i_V in component calcium_concentration
 * O in component O
 * alpha in component rate_constants
 * alpha_ in component rate_constants
 * beta in component rate_constants
 * beta_ in component rate_constants
 * kG_plus in component rate_constants
 * T in component rate_constants
 * d/dt V in component membrane
 * d/dt n in component potassium_current_n_gate
 * d/dt R in component transmitter_release
 * d/dt a in component rate_constants
 * d/dt C1 in component C1
 * d/dt C2 in component C2
 * d/dt C3 in component C3
 * d/dt C4 in component C4
 * d/dt C_G1 in component C_G1
 * d/dt C_G2 in component C_G2
 * d/dt C_G3 in component C_G3