A model showing the importance of the parameters characterizing ion transport through geometrically defined nanoslits filled with electrolyte is presented. A conductance plateau sin log-log scaled at low salt concentrations in the nanometer-sized apertures was both modeled and measured. This is due to the dominance of the effective surface charge density in the nanoslits inducing an excess of mobile counterions to maintain electroneutrality. The nanoslit conductance could be regulated at low salt concentrations by pH adjustment and by an external voltage applied on the chip. This effect can be exploited for ionic flow regulation in nanofluidic devices. (c) 2005 American Institute of Physics.