We consider topics of zero current for ionic flows via the Poisson-Nernst-Planck models. These include the study of reversal potential and reversal permanent charge. For ionic mixture of two ion species, our result on reversal potential extends significantly the Nernst equation, and the Goldman-Hodgkin-Katz equation for reversal potential. In particular, our study on the reversal potential includes effects of channel structure (its shape and its permanent charge) in addition to those of diffusion coefficients and boundary concentrations.