Coulomb Effects and Electron Transport Through a Coherent Conductor

We analyze electron transport through relatively short coherent conductors in the presence of Coulomb interaction. We evaluate the current-voltage characteristics of such conductors taking into account the effect of an external environment. Within our model, at large conductances and low $T$ the conductance is suppressed by a universal factor which depends only on the type of the conductor. We also argue that at T=0 the system ``scatterer+shunt'' can be either an insulator or a metal depending on whether its total resistance is larger or smaller than $R_Q=h/e^2\approx 25.8$ k$\Omega$. In a metallic phase the Coulomb gap is fully suppressed by quantum fluctuations.