Evidence for inorganic phosphate binding at nodes of Ranvier in peripheral nerves

Ferric ion is bound to different sites at nodes of Ranvier, depending on how the nerves are prepared. By immersing fresh, unfixed nerves in phosphate buffer, cacodylate buffer, or physiological saline prior to staining with ferric ion and ferrocyanide, it can be shown that binding of ferric ion to the extracellular nodal gap substance requires pretreatment with inorganic phosphate. This implies that phosphate anions are bound to the gap substance where they may then promote precipitation of ferric ion. These results call for a re-evaluation of data that depend on ferric ion binding to nodes of Ranvier. They also open the possibility that affinity for anions in general, or phosphate in particular, may be a significant feature of extracellular molecules present at nodes.