The effect of internal barium on the K current of the node of Ranvier.

Voltage clamp experiments were performed on single myelinated nerve fibres of the frog Rana esculenta to study the influence of internally applied Ba on the potassium outward current IK. Potassium currents of Ba-treated fibres decay rapidly during 30 ms depolarizations of more than 60 mV. The time constant tau of decay and the steady state potassium current IKss are strongly voltage dependent. The equilibrium dissociation constant K of the Ba-receptor complex decreases e-fold for a 39 mV change of potential. The analysis suggests that the binding site is located at 30% of the membrane field seen from the inside of the axon.