I_Ca I_K I_KCa I_KATP C_m 1 1 v_m V s_m g_Ca_ m_infinity V V_Ca 1 1 v_n V s_n n_infinity n tau_n g_K_ n V V_K 1 1 k_D c g_KCa_ omega V V_K ATP 1 k ADP 2 phi eta ADP 1000 tau_c v phi 1000 tau_c V V_K g_KATP_ ATP J_mem f alpha I_Ca k_c c