Ion regulation of the kinetics of potential-dependent potassium channels.

We apply a theoretical approach developed earlier. The interaction ofions that permeate a channel with slowly relaxing charged channel-forminggroups (ion-conformational interaction - ICI) is addressed by thisapproach. One can describe the ion concentration influence (ion regulation)on channel functioning in this manner. A patch-clamp method in a'whole-cell' configuration is used to study the ICI. For this purpose theinfluence of an external concentration of potassium ions on thepotential-dependent potassium current (I(A)) in the externalmembrane of GH(3) cells was studied. The increase of[K(+) (out)] from 5 mM to 100 mM causes anon-monotonous shift of current-voltage dependencies. The dependence of bothan activation time constant tgr(n) and a steady-state activation(n(∞)) on K(+) have a minimum andmaximum respectively. The analysis of the results suggests that the observedeffects are caused by ICI. A physical model is developed to describe thedependence of the potassium channel kinetics on the external concentrationof the ions and the membrane potential. The 'deformation' of the closedstate of the gate and the corresponding energy shifts cause the observednon-monotonous dependencies due to ICI. Thus, the general theoreticalapproach has an experimental confirmation and is applied to concreteexamples. Formulas for concentrational dependencies of the channel kineticsare given for practical uses.