  Ion transport in biological and synthetic nanochannels is characterized by
such phenomena as ion current fluctuations, rectification, and pumping.
Recently, it has been shown that the nanofabricated synthetic pores could be
considered as analogous to biological channels with respect to their transport
characteristics \cite{Apel, Siwy}. The ion current rectification is analyzed.
Ion transport through cylindrical nanopores is described by the Smoluchowski
equation. The model is considering the symmetric nanopore with asymmetric
charge distribution. In this model, the current rectification in asymmetrically
charged nanochannels shows a diode-like shape of $I-V$ characteristic. It is
shown that this feature may be induced by the coupling between the degree of
asymmetry and the depth of internal electric potential well. The role of
concentration gradient is discussed.
