Inactivation of the potassium transport system of myelinated nerve in the presence of a cyclic ionophore.

A potassium carrying ionophore dicyclohexano-18-crown-6 was found to affect the specific ionic currents in the node of Ranvier. Its presence caused an inactivation of the potassium permeability mechanism and a decrease of the sodium permeability. The rate of inactivation of the potassium permeability depended on crown ether concentration, on membrane potential and on temperature. At large concentrations, the rate of inactivation was of the same order of size as the normal rate of activation. The recovery from the inactivated state was slow, it took a few seconds, and recovery time depended on holding potential. The inactivation was caused by potential steps in positive direction. The uncomplexed crown ether is uncharged and does not move due to a potential gradient. The mechanism by which the crown ether makes the inactivation potential dependent remains obscure. A few other ionophores were tested but they did not affect the membrane currents.