Ion transport across biological membranes. Diffusion in water solution or conduction in the solid state?

The mechanism of the highly efficient and precisely regulated ion flux across axonal membranes has usually been considered as free diffusion in aqueous channels. The evidence for single-file mechanisms has not been convincing. In this report, solid-state ionic conductance is proposed as an alternative mechanism. The sequence of the Na+ 'channel' protein is scrutinized for elements that may form an ionic core that is well insulated by a hydrophobic mantle from other segments of the protein. A specific structure is proposed that may correspond to ionic lattices as they are known to exist in crystals of small, inorganic electrolytes that exhibit considerable ionic conduction.