Ion-exchange at the node of Ranvier

Synopisis A study has been made of the cation-binding capacity of nodal regions of rat peripheral nerve fibres. Material within the nodal gap was found to bind ferric (Fe³⁺), barium (Ba²⁺) and potassium (K⁺) ions, the affinity for cations decreasing with ionic valency. The nature of the bond to presumed fixed anionic sites at the node was deduced to be electrostatic, the strength of the bond depending on the charge of the cation and also probably on its hydrated ionic diameter. Cation-exchange was demonstrated at the node histochemically. Material with ion-exchange properties is presumed to overlay the free surface of the electrically excitable axon membrane at the nodal gap. The effects of a variety of enzymes and organic solvents on cation uptake at the node were determined and suggestions are made as to the chemical nature of the anionic binding sites. The physiological implications of these findings are discussed within the framework of present concepts concerning the conduction of the nervous impulse.