i_Ca i_K i_K_ATP i_s tau 1 1 V_m V theta_m g_Ca m_infinity V V_Ca lambda n_infinity n tau 1 1 V_n V theta_n g_K n V V_K s_infinity s tau_s 1 1 V_s V theta_s g_s s V V_K g_K_ATP p V V_K