Survival of K⁺ permeability and gating currents in squid axons perfused with K⁺-free media

K⁺ currents were recorded in squid axons internally perfused with impermeant electrolyte. Total absence of permeant ions inside and out leads to an irreversible loss of potassium conductance with a time constant of -11 min at 8°C. Potassium channels can be protected against this effect by external K⁺, Cs⁺, NH₄⁺, and Rb⁺ at concentrations of 100-440 mM. These experiments suggest that a K⁺ channel is normally occupied by one or more small cations, and becomes nonfunctional when these cations are removed. A large charge movement said to be related to K⁺ channel gating in frog skeletal muscle is absent in squid giant axons. However, deliberate destruction of K⁺ conductance by removal of permeant cations is accompanied by measurable loss in asymmetric charge movement. This missing charge component is large enough to contain a contribution from K+ gating charge movements of more than five elementary charges per channel.