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 (GK) irreversibly drops while the channels are maintained undisturbed at the holding potential. Herein it is reported that the drop of GK follows first-order kinetics, with a voltage-dependent decay rate r. Hyperpolarized potentials drastically inhibit the drop of GK. The GK 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, GK drops in 0 K+ with rates slower than those predicted based on the behavior of r at negative potentials, endowing the r-Vm 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 GK stabilization achieved at hyperpolarized potentials could be the result of a conformational change in the pore itself.