Stability of the Shab K+ channel conductance in 0 K+ solutions: the role of the membrane potential

Shab channels are fairly stable with K⁺ present on only one side of the membrane. However, on exposure to 0 K⁺ solutions on both sides of the membrane, the Shab K⁺ conductance (G_K) irreversibly drops while the channels are maintained undisturbed at the holding potential. Herein it is reported that the drop of G_K follows first-order kinetics, with a voltage-dependent decay rate r. Hyperpolarized potentials drastically inhibit the drop of G_K. The G_K drop at negative potentials cannot be explained by a shift in the voltage dependence of activation. At depolarized potentials, where the channels undergo a slow inactivation process, G_K drops in 0 K⁺ with rates slower than those predicted based on the behavior of r at negative potentials, endowing the r-V_m relationship with a maximum. Regardless of voltage, r is very small compared with the rate of ion permeation. Observations support the hypothesized presence of a stabilizing K⁺ site (or sites) located either within the pore itself or in its external vestibule, at an inactivation-sensitive location. It is argued that part of the G_K stabilization achieved at hyperpolarized potentials could be the result of a conformational change in the pore itself.