We explore the idea that the occurrence of nano-flares in the magnetic loop around the O VI formation temperature could explain the observed red-shift of mid-low transition region lines as well as the blue-shift observed in low coronal lines (T > 6 10^{5} K). Observations are compared to numerical simulations of the response of the solar atmosphere to an energy perturbation of 4 10^24 ergs representing an energy release during magnetic reconnection in a 1-D semi-circular flux tube. The temporal evolution of the thermodynamic state of the loop is converted into C IV 1548, O VI 1032 and Ne VIII 770 line profiles in non-equilibrium ionization. Performing an integration over the entire period of simulations, a red-shift of ~ 6 km s^{-1} is found in C IV, while a blue-shift of ~2 km s^{-1} and ~ 10 km s^{-1} were derived for O VI and Ne VIII, respectively, in resonable agreement with observations.